Rotating electrical machine and production method thereof

ABSTRACT

A rotating electrical machine is equipped with a rotor and a stator. The rotor includes a magnet unit and a rotor core retaining the magnet unit. The rotor core is made of a stack of annular core plates and an annular end plate mounted on an end of the stack of the core plates. The end plate has a deformable wave shape. The stack of the core plates and the end plate has formed therein through-holes extending through a length thereof. Bar-shaped fastening members, such as rivets, which have flanges on ends thereof are inserted into the through-holes with the flanges pressing the end plate to elastically deform the wave shape of the end plate, thereby tightly gripping the stack of the core plates in the lengthwise direction. This minimizes concentration of stress on the core plates to eliminate a risk of damage or breakage of the rotor.

CROSS REFERENCE TO RELATED DOCUMENT

The present application claims the benefit of priority of JapanesePatent Application No. 2019-114903 filed on Jun. 20, 2019, thedisclosure of which is incorporated herein by reference.

BACKGROUND 1 Technical Field

This disclosure relates generally to a rotating electrical machine and aproduction method thereof.

2 Background Art

IPM (Interior Permanent Magnet) rotors which have a rotor core made of astack of magnetic steel plates and magnets disposed in magnet chambersformed in the stator core are becoming widely used as rotatingelectrical machines. Magnets used in such a rotor may be implemented bythose taught in Japanese Patent Publication No. 2014-93859. The magnetsin this publication are each designed to create a surface magnetic fluxdensity approximating a sine wave which changes more gradually thanradial magnets, thereby resulting in a decrease in eddy current loss andalso enabling the magnetic flux density to be increased.

The stack of magnetic steel plates is usually compressed in a lengthwisedirection thereof using rivets or bolts. Each of the magnetic steelplates is usually thin. Tightly compressing the stack of the magneticsteel plate using the rivets or bolts, therefore, leads to a risk thatstress may concentrate on contacts between the rivets or bolts and themagnetic steel plates, so that the magnetic steel plate is damaged orbroken. In a case where the rotating electrical machine is used in avehicle, mechanical impact or vibration may be exerted on the rotatingelectrical machine, thereby leading to a risk that stress maytemporarily concentrate on the contacts between the rivets or bolts andthe magnetic steel plates, resulting in them being broken or undesirablydeformed.

SUMMARY

It is an object of this disclosure to provide a rotating electricalmachine designed to minimize concentration of stress on a core platethereof, and a production method thereof.

According to one aspect of this disclosure, there is provided a rotatingelectrical machine which comprises: (a) a magnetic field-producing unitwhich includes a magnet unit and a magnetic core, the magnet unit beingequipped with a plurality of magnetic poles arranged to have magneticpolarities located alternately in a circumferential direction of themagnetic field-producing unit; (b) an armature which is equipped with amulti-phase winding; and (c) a rotor which is implemented by one of themagnetic field-producing unit and the armature. The magnetic core ismade of a stack of a plurality of annular core plates and an annular endplate. The annular core plates are disposed on each other in a form of astack with axially opposed ends. The annular end plate is mounted on atleast one of the axially opposed ends of the stack of the annular coreplates. The core plates and the end plate have formed thereinthrough-holes which extend through the stack of the core plates and theend plate in an axial direction thereof. Fastening members which are ofa bar shape are disposed in the through-holes. Each of the fasteningmembers has a flange on an end of a length thereof. The flanges of thefastening members engage the end plate to tighten the core plates in theaxial direction. The end plate has a wave which is deformable in theaxial direction.

If the core plates are gripped and fixed by the fastening members withthe flanges of the fastening members placed in direct contact with thecore plates, it may case mechanical stress to concentrate on thecontacts. The core plates are usually thin. The concentration of stresson the core plates, therefore, it may result in breakage or bending ofthe core plates. In order to alleviate such a drawback, the stack of thecore plates is compressed by the flanges of the fastening membersthrough the end plate. The end plate disposed between the flanges of thefastening members and the stack of the core plates serves to diffuse thestress. The end plate is designed in the form of a wave to beelastically deformable in the lengthwise direction (i.e., the axialdirection) of the stack of the core plates. This enables air gaps to becreated between the end plate and an end of the stack of the core platesas cushions which absorb mechanical impact acting on the end plate,thereby minimizing mechanical damage to the stack of the core plates.

In the first preferred mode, the end plate is made of a rolled stripwhose outer side portion is milled or a curled plate strip formed bybending a plate strip in a circumferential direction of the end plate.

The above structure of the end plate facilitates the ease with which theend plates is machined to have the wave. The strip is machined into acircular ring shape, thereby enhancing the machining efficiency ascompared with when a disc plate is stamped to make the end plate.

In the second preferred mode, the through-holes are located closer to anouter peripheral edge of the end plate than to a radial center thereof.

If the through-holes are formed in the plate strip, after which theplate strip is machined into a circular ring shape, it will cause thethrough-holes to absorb distortion arising from the machining of theplate strip, thereby resulting in a decrease in amount by which the waveof the end plate is elastically deformed. When the plate strip ismachined into the circular ring shape, it will usually result in alarger degree of elastic deformation of a radially inner side of theplate strip than that of a radially outer side of the plate strip. Forthese reasons, the through-holes are formed close to the outerperipheral edge of the end plate after machined into the circular ringshape, thereby achieving a desired degree of elastic deformation of thewave of the end plate to ensure a required ability of the wavefunctioning as cushions.

According to another aspect of this disclosure, there is provided aproduction method for producing a rotating electrical machine whichincludes: (a) a magnetic field-producing unit which includes a magnetunit equipped with a plurality of magnetic poles arranged to havemagnetic polarities located alternately in a circumferential directionof the magnetic field-producing unit; (b) an armature which is equippedwith a multi-phase winding; and (c) a rotor which is implemented by oneof the magnetic field-producing unit and the armature. The methodcomprises: (a) preparing a first stack of a plurality of annular coreplates; (b) mounting an annular end plate on at least one of opposedends of a length of the first stack of the annular core plates to form asecond stack; (c) inserting bar-shaped fastening members intothrough-holes extending through the second stack in a lengthwisedirection thereof, each of the bar-shaped fastening member having aflange on an end thereof; (d) and tightening the fastening members tohave the flanges pressing the end plate to grip the second stack of thecore plates and the end plate to complete a magnetic core assembled withthe magnetic unit of the magnetic field-producing unit. The end platehas a wave deformable in a lengthwise direction of the second stack.

The end plate disposed between the flanges of the fastening members andthe stack of the core plates serves to diffuse the stress. The end plateis designed in the form of a wave to be elastically deformable in thelengthwise direction (i.e., the axial direction) of the stack of thecore plates. This enables air gaps to be created between the end plateand an end of the stack of the core plates as cushions which absorbmechanical impact acting on the end plate, thereby minimizing mechanicaldamage to the stack of the core plates.

In the first preferred mode of the production method, the end plate ismade by milling one of outer side portions of a width of a strip or bybending a strip in a circumferential direction of the end plate.

The above structure of the end plate facilitates the ease with which theend plates is waved in the circumferential direction. The strip ismachined into a circular ring shape, thereby enhancing the machiningefficiency as compared with when a disc plate is stamped to make the endplate.

In the second preferred mode of the production method, the through-holesare formed in the one of the outer side portions of the strip, afterwhich the strip is machined to complete the end plate.

The above structure achieves an increased degree of elastic deformationof the wave of the end plate to ensure a required ability of the wavefunctioning as cushions.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given hereinbelow and from the accompanying drawings of thepreferred embodiments of the invention, which, however, should not betaken to limit the invention to the specific embodiments but are for thepurpose of explanation and understanding only.

In the drawings:

FIG. 1 is a perspective longitudinal sectional view of a rotatingelectrical machine;

FIG. 2 is a longitudinal sectional view of a rotating electricalmachine;

FIG. 3 is a sectional view taken along the line III-III in FIG. 2;

FIG. 4 is a partially enlarged sectional view of FIG. 3;

FIG. 5 is an exploded view of a rotating electrical machine;

FIG. 6 is an exploded view of an inverter unit;

FIG. 7 is a torque diagrammatic view which demonstrates a relationshipbetween ampere-turns and torque density in a stator winding;

FIG. 8 is a transverse sectional view of a rotor and a stator;

FIG. 9 is an enlarged view of part of FIG. 8;

FIG. 10 is a transverse sectional view of a stator;

FIG. 11 is a longitudinal sectional view of a stator;

FIG. 12 is a perspective view of a stator winding;

FIG. 13 is a perspective view of a conductor;

FIG. 14 is a schematic view illustrating a structure of wire;

FIGS. 15(a) and 15(b) are views showing the layout of conductors at then^(th) layer position;

FIG. 16 is a side view showing conductors at the n^(th) layer positionand the (n+1)^(th) layer position;

FIG. 17 is a view representing a relation between an electrical angleand a magnetic flux density in magnets of an embodiment;

FIG. 18 is a view which represents a relation between an electricalangle and a magnetic flux density in a comparative example of magnetarrangement;

FIG. 19 is an electrical circuit diagram of a control system for arotating electrical machine;

FIG. 20 is a functional block diagram which shows a current feedbackcontrol operation of a control device;

FIG. 21 is a functional block diagram which shows a torque feedbackcontrol operation of a control device;

FIG. 22 is a transverse sectional view of a rotor and a stator in thesecond embodiment;

FIG. 23 is a partially enlarged view of FIG. 22;

FIGS. 24(a) and 24(b) are views demonstrating flows of magnetic flux ina magnet unit;

FIG. 25 is a sectional view of a stator in the first modification;

FIG. 26 is a sectional view of a stator in the first modification;

FIG. 27 is a sectional view of a stator in the second modification;

FIG. 28 is a sectional view of a stator in the third modification;

FIG. 29 is a sectional view of a stator in the fourth modification;

FIG. 30 is a sectional view of a stator in the seventh modification;

FIG. 31 is a functional block diagram which illustrates a portion ofoperations of an operation signal generator in the eighth modification8;

FIG. 32 is a flowchart representing a sequence of steps to execute acarrier frequency altering operation;

FIG. 33(a) is a view which illustrates connections of conductorsconstituting a conductor group in the first and second embodiments.

FIG. 33(b) is a view which illustrates connections of conductorsconstituting a conductor group in the ninth modification.

FIG. 33(c) is a view which illustrates connections of conductorsconstituting a conductor group in a variation of the ninth modification.

FIG. 34 is a view which illustrates a stack of four conductors in theninth modification;

FIG. 35 is a transverse sectional view of an inner rotor type rotor anda stator in the tenth modification;

FIG. 36 is a partially enlarged view of FIG. 35;

FIG. 37 is a longitudinal sectional view of an inner rotor type rotatingelectrical machine;

FIG. 38 is a longitudinal sectional view which schematically illustratesa structure of an inner rotor type rotating electrical machine;

FIG. 39 is a view which illustrates a structure of an inner rotor typerotating electrical machine in the eleventh modification;

FIG. 40 is a view which illustrates a structure of an inner rotor typerotating electrical machine in the eleventh modification;

FIG. 41 is a view which illustrates a structure of a revolving armaturetype of rotating electrical machine in the twelfth modification;

FIG. 42 is a sectional view which illustrates a structure of a conductorin the fourteenth modification;

FIG. 43 is a view which illustrates a relation among reluctance torque,magnet torque, and distance DM;

FIG. 44 is a view which illustrates teeth;

FIG. 45 is a perspective view which illustrates a structure of a wheelassembly with an in-wheel motor and a peripheral structure;

FIG. 46 is a longitudinal sectional view which illustrates a wheelassembly and a peripheral structure;

FIG. 47 is an exploded view of a wheel assembly;

FIG. 48 is a side view which illustrates a rotating electrical machine,as viewed from a protruding portion of a rotating shaft;

FIG. 49 is a sectional view taken along the line 49-49 in FIG. 48;

FIG. 50 is a sectional view taken along the line 50-50 in FIG. 49;

FIG. 51 is an exploded sectional view of a rotating electrical machine;

FIG. 52 is a partially sectional view of a rotor;

FIG. 53 is a perspective view of a stator winding and a stator core;

FIGS. 54(a) and 54(b) are front views which illustrate a development ofa stator winding;

FIG. 55 is a view which demonstrates skew of a conductor;

FIG. 56 is an exploded sectional view of an inverter unit;

FIG. 57 is an exploded sectional view of an inverter unit;

FIG. 58 is a view which demonstrates layout of electrical modules in aninverter housing;

FIG. 59 is a circuit diagram which illustrates an electrical structureof a power converter;

FIG. 60 is a sectional view which illustrates a cooling structure of aswitch module;

FIGS. 61(a) and 61(b) are sectional views which illustrate a coolingstructure of a switch module;

FIGS. 62(a), 62(b), and 62(c) are partial views which illustrate acooling structure of a switch module;

FIGS. 63(a) and 63(b) are partially sectional views each of whichillustrates a cooling structure of a switch module;

FIG. 64 is a partial view which illustrates a cooling structure of aswitch module;

FIG. 65 is a view which illustrates layout of electrical modules and acoolant path;

FIG. 66 is a sectional view taken along the line 66-66 in FIG. 49;

FIG. 67 is a sectional view taken along the line 67-67 in FIG. 49;

FIG. 68 is a perspective view which illustrates a bus bar module;

FIG. 69 is a circuit diagram which illustrates a relation in electricalconnection between electrical modules and a bus bar module;

FIG. 70 is a view which illustrates electrical connections betweenelectrical modules and a bus bar module;

FIG. 71 is a view which illustrates electrical connections betweenelectrical modules and a bus bar module;

FIGS. 72(a), 72(b), 72(c), and 72(d) are structural views of the firstmodified form of an in-wheel motor;

FIGS. 73(a), 73(b), and 73(c) are structural views of the secondmodified form of an in-wheel motor;

FIGS. 74(a) and 74(b) are structural views of the third modified form ofan in-wheel motor;

FIG. 75 is a structural view of the fourth modified form of an in-wheelmotor;

FIG. 76 is a transverse sectional view which illustrates a rotor and astator in the fifteenth modification;

FIG. 77 is a partially enlarged view of the rotor and the stator in FIG.76;

FIG. 78 is a longitudinally sectional view of a rotor in the fifteenthmodification;

FIG. 79 is a plan view which illustrates an end plate assembled with astator core in the fifteenth modification;

FIG. 80(a) is a partially sectional view which illustrates an end platesecured to a stack of core plates in the fifteenth modification;

FIG. 80(b) is a partially sectional view which illustrates the end platebefore secured to the stack of core plates in FIG. 80(a);

FIG. 81 is a schematically explanatory view which demonstrates aproduction method of an end plate for use in stacking core plates; and

FIG. 82 is a partially transverse sectional view which illustratesvariants of a rotor and a stator in the fifteenth modification.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

The embodiments will be described below with reference to the drawings.Parts of the embodiments functionally or structurally corresponding toeach other or associated with each other will be denoted by the samereference numbers or by reference numbers which are different in thehundreds place from each other. The corresponding or associated partsmay refer to the explanation in the other embodiments.

The rotating electrical machine in the embodiments is configured to beused, for example, as a power source for vehicles. The rotatingelectrical machine may, however, be used widely for industrial,automotive, domestic, office automation, or game applications. In thefollowing embodiments, the same or equivalent parts will be denoted bythe same reference numbers in the drawings, and explanation thereof indetail will be omitted.

First Embodiment

The rotating electrical machine 10 in this embodiment is a synchronouspolyphase ac motor having an outer rotor structure (i.e., an outerrotating structure). The outline of the rotating electrical machine 10is illustrated in FIGS. 1 to 5. FIG. 1 is a perspective longitudinalsectional view of the rotating electrical machine 10. FIG. 2 is alongitudinal sectional view along the rotating shaft 11 of the rotatingelectrical machine 10. FIG. 3 is a transverse sectional view (i.e.,sectional view taken along the line III-III in FIG. 2) of the rotatingelectrical machine 10 perpendicular to the rotating shaft 11. FIG. 4 isa partially enlarged sectional view of FIG. 3. FIG. 5 is an explodedview of the rotating electrical machine 10. FIG. 3 omits hatchingshowing a section except the rotating shaft 11 for the sake ofsimplicity of the drawings. In the following discussion, a lengthwisedirection of the rotating shaft 11 will also be referred to as an axialdirection. A radial direction from the center of the rotating shaft 11will be simply referred to as a radial direction. A direction along acircumference of the rotating shaft 11 about the center thereof will besimply referred to as a circumferential direction.

The rotating electrical machine 10 includes the bearing unit 20, thehousing 30, the rotor 40, the stator 50, and the inverter unit 60. Thesemembers are arranged coaxially with each other together with therotating shaft 11 and assembled in a given sequence to complete therotating electrical machine 10. The rotating electrical machine 10 inthis embodiment is equipped with the rotor 40 working as a magneticfield-producing unit or a field system and the stator 50 working as anarmature and engineered as a revolving-field type rotating electricalmachine.

The bearing unit 20 includes two bearings 21 and 22 arranged away fromeach other in the axial direction and the retainer 23 which retains thebearings 21 and 22. The bearings 21 and 22 are implemented by, forexample, radial ball bearings each of which includes the outer race 25,the inner race 26, and a plurality of balls 27 disposed between theouter race 25 and the inner race 26. The retainer 23 is of a cylindricalshape. The bearings 21 and 22 are disposed radially inside the retainer23. The rotating shaft 11 and the rotor 40 are retained radially insidethe bearings 21 and 22 to be rotatable. The bearings 21 and 22 are usedas a set of bearings to rotatably retain the rotating shaft 11.

Each of the bearings 21 and 22 holds the balls 27 using a retainer, notshown, to keep a pitch between the balls 27 constant. Each of thebearings 21 and 22 is equipped with seals on axially upper and lowerends of the retainer and also has non-conductive grease (e.g.,non-conductive urease grease) installed inside the seals. The positionof the inner race 26 is mechanically secured by a spacer to exertconstant inner precompression on the inner race 26 in the form of avertical convexity.

The housing 30 includes the cylindrical peripheral wall 31. Theperipheral wall 31 has a first end and a second end opposed to eachother in an axial direction thereof. The peripheral wall 31 has the endsurface 32 on the first end and the opening 33 in the second end. Theopening 33 occupies the entire area of the second end. The end surface32 has formed in the center thereof the circular hole 34. The bearingunit 20 is inserted into the hole 34 and fixed using a fastener, such asa screw or a rivet. The hollow cylindrical rotor 40 and the hollowcylindrical stator 50 are disposed in an inner space defined by theperipheral wall 31 and the end surface 32 within the housing 30. In thisembodiment, the rotating electrical machine 10 is of an outer rotortype, so that the stator 50 is arranged radially inside the cylindricalrotor 40 within the housing 30. The rotor 40 is retained in a cantileverform by a portion of the rotating shaft 11 close to the end surface 32in the axial direction.

The rotor 40 includes the hollow cylindrical magnetic holder 41 and theannular magnet unit 42 disposed radially inside the magnet holder 41.The magnet holder 41 is of substantially a cup-shape and works as amagnet holding member. The magnet holder 41 includes the cylinder 43,the attaching portion 44 which is of a cylindrical shape and smaller indiameter than the cylinder 43, and the intermediate portion 45connecting the cylinder 43 and the attaching portion 44 together. Thecylinder 43 has the magnet unit 42 secured to an inner peripheralsurface thereof.

The magnet holder 41 is made of cold rolled steel (SPCC), forging steel,or carbon fiber reinforced plastic (CFRP) which have a required degreeof mechanical strength.

The rotating shaft 11 passes through the through-hole 44 a of theattaching portion 44. The attaching portion 44 is secured to a portionof the rotating shaft 11 disposed inside the through-hole 44 a. In otherwords, the magnet holder 41 is secured to the rotating shaft 11 throughthe attaching portion 44. The attaching portion 44 may preferably bejoined to the rotating shaft 11 using concavities and convexities, suchas a spline joint or a key joint, welding, or crimping, so that therotor 40 rotates along with the rotating shaft 11.

The bearings 21 and 22 of the bearing unit 20 are secured radiallyoutside the attaching portion 44. The bearing unit 20 is, as describedabove, fixed on the end surface 32 of the housing 30, so that therotating shaft 11 and the rotor 40 are retained by the housing 30 to berotatable. The rotor 40 is, thus, rotatable within the housing 30.

The rotor 40 is equipped with the attaching portion 44 arranged only oneof ends thereof opposed to each other in the axial direction of therotor 40. This cantilevers the rotor 40 on the rotating shaft 11. Theattaching portion 44 of the rotor 40 is rotatably retained at two pointsof supports using the bearings 21 and 22 of the bearing unit 20 whichare located away from each other in the axial direction. In other words,the rotor 40 is held to be rotatable using the two bearings 21 and 22which are separate at a distance away from each other in the axialdirection on one of the axially opposed ends of the magnet holder 41.This ensures the stability in rotation of the rotor 40 even though therotor 40 is cantilevered on the rotating shaft 11. The rotor 40 isretained by the bearings 21 and 22 at locations which are away from thecenter intermediate between the axially opposed ends of the rotor 40 inthe axial direction thereof.

The bearing 22 of the bearing unit 20 which is located closer to thecenter of the rotor 40 (a lower one of the bearings 21 and 22 in thedrawings) is different in dimension of a gap between each of the outerrace 25 and the inner race and the balls 27 from the bearing 21 which islocated farther away from the center of the rotor 40 (i.e., an upper oneof the bearings 21 and 22). For instance, the bearing 22 closer to thecenter of the rotor 40 is greater in the dimension of the gap from thebearing 21. This minimizes adverse effects on the bearing unit 20 whicharise from deflection of the rotor 40 or mechanical vibration of therotor 40 due to imbalance resulting from parts tolerance at a locationclose to the center of the rotor 40. Specifically, the bearing 22 closerto the center of the rotor 40 is engineered to have dimensions of thegaps or plays increased using precompression, thereby absorbing thevibration generating in the cantilever structure. The precompression maybe provided by either fixed position preload or constant pressurepreload. In the case of the fixed position preload, the outer race 25 ofeach of the bearings 21 and 22 is joined to the retainer 23 usingpress-fitting or welding. The inner race 26 of each of the bearings 21and 22 is joined to the rotating shaft 11 by press-fitting or welding.The precompression may be created by placing the outer race 25 of thebearing 21 away from the inner race 26 of the bearing 21 in the axialdirection or alternatively placing the outer race 25 of the bearing 22away from the inner race 26 of the bearing 22 in the axial direction.

In the case of the constant pressure preload, a preload spring, such asa wave washer 24, is arranged between the bearing 22 and the bearing 21to create the preload directed from a region between the bearing 22 andthe bearing 21 toward the outer race 25 of the bearing 22 in the axialdirection. In this case, the inner race 26 of each of the bearing 21 andthe bearing 22 is joined to the rotating shaft 11 using press fitting orbonding. The outer race 25 of the bearing 21 or the bearing 22 isarranged away from the outer race 25 through a given clearance. Thisstructure exerts pressure, as produced by the preload spring, on theouter race 25 of the bearing 22 to urge the outer race 25 away from thebearing 21. The pressure is then transmitted through the rotating shaft11 to urge the inner race 26 of the bearing 21 toward the bearing 22,thereby bringing the outer race 25 of each of the bearings 21 and 22away from the inner race 26 thereof in the axial direction to exert thepreload on the bearings 21 and 22 in the same way as the fixed positionpreload.

The constant pressure preload does not necessarily need to exert thespring pressure, as illustrated in FIG. 2, on the outer race 25 of thebearing 22, but may alternatively be created by exerting the springpressure on the outer race 25 of the bearing 21. The exertion of thepreload on the bearings 21 and 22 may alternatively be achieved byplacing the inner race 26 of one of the bearings 21 and 22 away from therotating shaft 11 through a given clearance therebetween and joining theouter race 25 of each of the bearings 21 and 22 to the retainer 23 usingpress-fitting or bonding.

Further, in the case where the pressure is created to bring the innerrace 26 of the bearing 21 away from the bearing 22, such pressure ispreferably additionally exerted on the inner race 26 of the bearing 22away from the bearing 21. Conversely, in the case where the pressure iscreated to bring the inner race 26 of the bearing 21 close to thebearing 22, such pressure is preferably additionally exerted on theinner race 26 of the bearing 22 to bring it close to the bearing 21.

In a case where the rotating electrical machine 10 is used as a powersource for a vehicle, there is a risk that mechanical vibration having acomponent oriented in a direction in which the preload is created may beexerted on the preload generating structure or that a direction in whichthe force of gravity acts on an object to which the preload is appliedmay be changed. In order to alleviate such a problem, the fixed positionpreload is preferably used in the case where the rotating electricalmachine 10 is mounted in the vehicle.

The intermediate portion 45 includes the annular inner shoulder 49 a andthe annular outer shoulder 49 b. The outer shoulder 49 b is arrangedoutside the inner shoulder 49 a in the radial direction of theintermediate portion 45. The inner shoulder 49 a and the outer shoulder49 b are separate from each other in the axial direction of theintermediate portion 45. This layout results in a partial overlapbetween the cylinder 43 and the attaching portion 44 in the radialdirection of the intermediate portion 45. In other words, the cylinder43 protrudes outside a base end portion (i.e., a lower portion, asviewed in the drawing) of the attaching portion 44 in the axialdirection. The structure in this embodiment enables the rotor 40 to beretained by the rotating shaft 11 at a location closer to the center ofgravity of the rotor 40 than a case where the intermediate portion 45 isshaped to be flat without any shoulder, thereby ensuring the stabilityin operation of the rotor 40.

In the above described structure of the intermediate portion 45, therotor 40 has the annular bearing housing recess 46 which is formed in aninner portion of the intermediate portion 45 and radially surrounds theattaching portion 44. The bearing housing recess 46 has a portion of thebearing unit 20 disposed therein. The rotor 40 also has the coil housingrecess 47 which is formed in an outer portion of the intermediateportion 45 and radially surrounds the bearing housing recess 46. Thecoil housing recess 47 has disposed therein the coil end 54 of thestator winding 51 of the stator 50, which will be described later indetail. The housing recesses 46 and 47 are arranged adjacent each otherin the axial direction. In other words, a portion of the bearing unit 20is laid to overlap the coil end 54 of the stator winding 51 in the axialdirection. This enables the rotating electrical machine 10 to have alength decreased in the axial direction.

The intermediate portion 45 extends or overhangs outward from therotating shaft 11 in the radial direction. The intermediate portion 45is equipped with a contact avoider which extends in the axial directionand avoids a physical contact with the coil end 54 of the stator winding51 of the stator 50. The intermediate portion 45 will also be referredto as an overhang.

The coil end 54 may be bent radially inwardly or outwardly to have adecreased axial dimension, thereby enabling the axial length of thestator 50 to be decreased. A direction in which the coil end 54 is bentis preferably determined depending upon installation thereof in rotor40. In the case where the stator 50 is installed radially inside therotor 40, a portion of the coil end 54 which is inserted into the rotor40 is preferably bent radially inwardly. A coil end opposite the coilend 54 may be bent either inwardly or outwardly, but is preferably bentto an outward side where there is an enough space in terms of theproduction thereof.

The magnet unit 42 working as a magnetic portion is made up of aplurality of permanent magnets which are disposed radially inside thecylinder 43 to have different magnetic poles arranged alternately in acircumferential direction thereof. The magnet unit 42, thus, has aplurality of magnetic poles arranged in the circumferential direction.The magnet unit 42 will also be described later in detail.

The stator 50 is arranged radially inside the rotor 40. The stator 50includes the stator winding 51 wound in a substantially cylindrical(annular) form and the stator core 52 used as a base member arrangedradially inside the stator winding 51. The stator winding 51 is arrangedto face the annular magnet unit 42 through a given air gap therebetween.The stator winding 51 includes a plurality of phase windings each ofwhich is made of a plurality of conductors which are arranged at a givenpitch away from each other in the circumferential direction and joinedtogether. In this embodiment, two three-phase windings: one including aU-phase winding, a V-phase winding, and a W-phase winging and the otherincluding an X-phase winding, a Y-phase winding, and a Z-phase windingare used to complete the stator winding 51 as a six-phase winding.

The stator core 52 is formed by an annular stack of magnetic steelplates made of soft magnetic material and mounted radially inside thestator winding 51. The magnetic steel plates are, for example, siliconnitride steel plates made by adding a small percent (e.g., 3%) ofsilicon nitride to iron. The stator winding 51 corresponds to anarmature winding. The stator core 52 corresponds to an armature core.

The stator winding 51 overlaps the stator core 52 in the radialdirection and includes the coil side portion 53 disposed radiallyoutside the stator core 52 and the coil ends 54 and 55 overhanging atends of the stator core 52 in the axial direction. The coil side portion53 faces the stator core 52 and the magnet unit 42 of the rotor 40 inthe radial direction. The stator 50 is arranged inside the rotor 40. Thecoil end 54 that is one (i.e., an upper one, as viewed in the drawings)of the axially opposed coil ends 54 and 55 and arranged close to thebearing unit 20 is disposed in the coil housing recess 47 defined by themagnet holder 41 of the rotor 40. The stator 50 will also be describedlater in detail.

The inverter unit 60 includes the unit base 61 secured to the housing 30using fasteners, such as bolts, and a plurality of electrical components62 mounted on the unit base 61. The unit base 61 is made from, forexample, carbon fiber reinforced plastic (CFRP). The unit base 61includes the end plate 63 secured to an edge of the opening 33 of thehousing 30 and the casing 64 which is formed integrally with the endplate 63 and extends in the axial direction. The end plate 63 has thecircular opening 65 formed in the center thereof. The casing 64 extendsupward from a peripheral edge of the opening 65.

The stator 50 is arranged on an outer peripheral surface of the casing64. Specifically, an outer diameter of the casing 64 is selected to beidentical with or slightly smaller than an inner diameter of the statorcore 52. The stator core 52 is attached to the outer side of the casing64 to complete a unit made up of the stator 50 and the unit base 61. Theunit base 61 is secured to the housing 30, so that the stator 50 isunified with the housing 50 in a condition where the stator core 52 isinstalled on the casing 64.

The stator core 52 may be bonded, shrink-fit, or press-fit on the unitbase 61, thereby eliminating positional shift of the stator core 52relative to the unit base 61 both in the circumferential direction andin the axial direction.

The casing 64 has a radially inner storage space in which the electricalcomponents 62 are disposed. The electrical components 62 are arranged tosurround the rotating shaft 11 within the storage space. The casing 64functions as a storage space forming portion. The electrical components62 include the semiconductor modules 66, the control board 67, and thecapacitor module 68 which constitute an inverter circuit.

The unit base 61 serves as a stator holder (i.e., an armature holder)which is arranged radially inside the stator 50 and retains the stator50. The housing 30 and the unit base 61 define a motor housing for therotating electrical machine 10. In the motor housing, the retainer 23 issecured to a first end of the housing 30 which is opposed to a secondend of the housing 30 through the rotor 40 in the axial direction. Thesecond end of the housing 30 and the unit base 61 are joined together.For instance, in an electric-powered vehicle, such as an electricautomobile, the motor housing is attached to a side of the vehicle toinstall the rotating electrical machine 10 in the vehicle.

The inverter unit 60 will be also be described using FIG. 6 that is anexploded view in addition to FIGS. 1 to 5.

The casing 64 of the unit base 61 includes the cylinder 71 and the endsurface 72 that is one of ends of the cylinder 71 which are opposed toeach other in the axial direction of the cylinder 71 (i.e., the end ofthe casing 64 close to the bearing unit 20). The end of the cylinder 71opposed to the end surface 72 in the axial direction is shaped to fullyopen to the opening 65 of the end plate 63. The end surface 72 hasformed in the center thereof the circular hole 73 through which therotating shaft 11 is insertable. The hole 73 has fitted therein thesealing member 171 which hermetically seals an air gap between the hole73 and the outer periphery of the rotating shaft 11. The sealing member171 is preferably implemented by, for example, a resinous slidable seal.

The cylinder 71 of the casing 64 serves as a partition which isolatesthe rotor 40 and the stator 50 arranged radially outside the cylinder 71from the electrical components 62 arranged radially inside the cylinder71. The rotor 40, the stator 50, and the electrical components 62 arearranged radially inside and outside the cylinder 71.

The electrical components 62 are electrical devices making up theinverter circuit equipped with a motor function and a generatorfunction. The motor function is to deliver electrical current to thephase windings of the stator winding 51 in a given sequence to turn therotor 40. The generator function is to receive a three-phase ac currentflowing through the stator winding 51 in response to the rotation of therotating shaft 11 and generate and output electrical power. Theelectrical components 62 may be engineered to perform either one of themotor function and the generator function. In a case where the rotatingelectrical machine 10 is used as a power source for a vehicle, thegenerator function provides a regenerative function to output aregenerated electrical power.

Specifically, the electrical components 62, as demonstrated in FIG. 4,include the hollow cylindrical capacitor module 68 arranged around therotating shaft 11 and the semiconductor modules 66 mounted on thecapacitor module 68. The capacitor module 68 has a plurality ofsmoothing capacitors 68 a connected in parallel to each other.Specifically, each of the capacitors 68 a is implemented by astacked-film capacitor which is made of a plurality of film capacitorsstacked in a trapezoidal shape in cross section. The capacitor module 68is made of the twelve capacitors 68 a arranged in an annular shape.

The capacitors 68 a may be produced by preparing a long film which has agiven width and is made of a stack of films and cutting the long filminto isosceles trapezoids each of which has a height identical with thewidth of the long film and whose short bases and long bases arealternately arranged. Electrodes are attached to the thus producedcapacitor devices to complete the capacitors 68 a.

The semiconductor module 66 includes, for example, a semiconductorswitch, such as a MOSFET or an IGBT and is of substantially a planarshape. In this embodiment, the rotating electrical machine 10 is, asdescribed above, equipped with two sets of three-phase windings and hasthe inverter circuits, one for each set of the three-phase windings. Theelectrical components 62, therefore, include a total of twelvesemiconductor modules 66 which are arranged in an annular form to makeup the semiconductor module group 66A.

The semiconductor modules 66 are interposed between the cylinder 71 ofthe casing 64 and the capacitor module 68. The semiconductor modulegroup 66A has an outer peripheral surface placed in contact with aninner peripheral surface of the cylinder 71. The semiconductor modulegroup 66A also has an inner peripheral surface placed in contact with anouter peripheral surface of the capacitor module 68. This causes heat,as generated in the semiconductor modules 66, to be transferred to theend plate 63 through the casing 64, so that it is dissipated from theend plate 63.

The semiconductor module group 66A preferably has the spacers 69disposed radially outside the outer peripheral surface thereof, i.e.,between the semiconductor modules 66 and the cylinder 71. A combinationof the capacitor modules 68 is so arranged as to have a regulardodecagonal section extending perpendicular to the axial directionthereof, while the inner periphery of the cylinder 71 has a circulartransverse section. The spacers 69 are, therefore, each shaped to have aflat inner peripheral surface and a curved outer peripheral surface. Thespacers 69 may alternatively be formed integrally with each other in anannular shape and disposed radially outside the semiconductor modulegroup 66A. The spacers 69 are highly thermally conductive and made of,for example, metal, such as aluminum or heat dissipating gel sheet. Theinner periphery of the cylinder 71 may alternatively be shaped to have adodecagonal transverse section like the capacitor modules 68. In thiscase, the spacers 69 are each preferably shaped to have a flat innerperipheral surface and a flat outer peripheral surface.

In this embodiment, the cylinder 71 of the casing 64 has formed thereinthe coolant path 74 through which coolant flows. The heat generated inthe semiconductor modules 66 is also released to the coolant flowing inthe coolant path 74. In other words, the casing 64 is equipped with acooling mechanism. The coolant path 74 is, as clearly illustrated inFIGS. 3 and 4, formed in an annular shape and surrounds the electricalcomponents 62 (i.e., the semiconductor modules 66 and the capacitormodule 68). The semiconductor modules 66 are arranged along the innerperipheral surface of the cylinder 71. The coolant path 74 is laid tooverlap the semiconductor modules 66 in the radial direction.

The stator 50 is arranged outside the cylinder 71. The electricalcomponents 62 are arranged inside the cylinder 71. This layout causesthe heat to be transferred from the stator 50 to the outer side of thecylinder 71 and also transferred from the electrical components 62(e.g., the semiconductor modules 66) to the inner side of the cylinder71. It is possible to simultaneously cool the stator 50 and thesemiconductor modules 66, thereby facilitating dissipation of thermalenergy generated by heat-generating members of the rotating electricalmachine 10.

Further, at least one of the semiconductor modules 66 which constitutepart or all of the inverter circuits serving to energize the statorwinding 51 to drive the rotating electrical machine is arranged in aregion surrounded by the stator core 52 disposed radially outside thecylinder 71 of the casing 64. Preferably, one of the semiconductormodules 66 may be arranged fully inside the region surrounded by thestator core 52. More preferably, all the semiconductor modules 66 may bearranged fully in the region surrounded by the stator core 52.

At least a portion of the semiconductor modules 66 is arranged in aregion surrounded by the coolant path 74. Preferably, all thesemiconductor modules 66 may be arranged in a region surrounded by theyoke 141.

The electrical components 62 include the insulating sheet 75 disposed onone of axially opposed end surfaces of the capacitor module 68 and thewiring module 76 disposed on the other end surface of the capacitormodule 68. The capacitor module 68 has two axially-opposed end surfaces:a first end surface and a second end surface. The first end surface ofthe capacitor module 68 closer to the bearing unit 20 faces the endsurface 72 of the casing 64 and is laid on the end surface 72 throughthe insulating sheet 75. The second end surface of the capacitor module68 closer to the opening 65 has the wiring module 76 mounted thereon.

The wiring module 76 includes the resin-made circular plate-shaped body76 a and a plurality of bus bars 76 b and 76 c embedded in the body 76a. The bus bars 76 b and 76 c electrically connect the semiconductormodules 66 and the capacitor module 68 together. Specifically, thesemiconductor modules 66 are equipped with the connecting pins 66 aextending from axial ends thereof. The connecting pins 66 a connect withthe bus bars 76 b radially outside the body 76 a. The bus bars 76 cextend away from the capacitor module 68 radially outside the body 76 aand have top ends connecting with the wiring members 79 (see FIG. 2).

The capacitor module 68, as described above, has the insulating sheet 75mounted on the first end surface thereof. The capacitor module 68 alsohas the wiring module 76 mounted on the second end surface thereof. Thecapacitor module 68, therefore, has two heat dissipating paths whichextend from the first and second end surfaces of the capacitor module 68to the end surface 72 and the cylinder 71. Specifically, the heatdissipating path is defined which extends from the first end surface tothe end surface 72. The heat dissipating path is defined which extendsfrom the second end surface to the cylinder 71. This enables the heat tobe released from the end surfaces of the capacitor module 68 other thanthe outer peripheral surface on which the semiconductor modules 66 arearranged. In other words, it is possible to dissipate the heat not onlyin the radial direction, but also in the axial direction.

The capacitor module 68 is of a hollow cylindrical shape and has therotating shaft 11 arranged therewithin at a given interval away from theinner periphery of the capacitor module 68, so that heat generated bythe capacitor module 68 will be dissipated from the hollow cylindricalspace. The rotation of the rotating shaft 11 usually produces a flow ofair, thereby enhancing cooling effects.

The wiring module 76 has the disc-shaped control board 67 attachedthereto. The control board 67 includes a printed circuit board (PCB) onwhich given wiring patterns are formed and also has ICs and the controldevice 77 mounted thereon. The control device 77 serves as a controllerand is made of a microcomputer. The control board 67 is secured to thewiring module 76 using fasteners, such as screws. The control board 67has formed in the center thereof the hole 67 a through which therotating shaft 11 passes.

The wiring module 76 has a first surface and a second surface opposed toeach other in the axial direction, that is, a thickness-wise directionof the wiring module 76. The first surface faces the capacitor module68. The wiring module 76 has the control board 67 mounted on the secondsurface thereof. The bus bars 76 c of the wiring module 76 extend fromone of surfaces of the control board 67 to the other. The control board67 may have cut-outs for avoiding physical interference with the busbars 76 c. For instance, the control board 67 may have the cut-outsformed in portions of the circular outer edge thereof.

The electrical components 62 are, as described already, arranged insidethe space surrounded by the casing 64. The housing 30, the rotor 40, andthe stator 50 are disposed outside the space in the form of layers. Thisstructure serves to shield against electromagnetic noise generated inthe inverter circuits. Specifically, the inverter circuit works tocontrol switching operations of the semiconductor modules 66 in a PWMcontrol mode using a given carrier frequency. The switching operationsusually generate electromagnetic noise against which the housing 30, therotor 40, and the stator 50 which are arranged outside the electricalcomponents 62 shield.

Further, at least a portion of the semiconductor modules 66 is arrangedinside the region surrounded by the stator core 52 located radiallyoutside the cylinder 71 of the casing 64, thereby minimizing adverseeffects of magnetic flux generated by the semiconductor modules 66 onthe stator winding 51 as compared with a case where the semiconductormodules 66 and the stator winding 51 are arranged without the statorcore 52 interposed therebetween. The magnetic flux created by the statorwinding 51 also hardly affects the semiconductor modules 66. It is moreeffective that the whole of the semiconductor modules 66 are located inthe region surrounded by the stator core 52 disposed radially outsidethe cylinder 71 of the casing 64. When at least a portion of thesemiconductor modules 66 is surrounded by the coolant path 74, it offersa beneficial advantage that the heat produced by the stator winding 51or the magnet unit 42 is prevented from reaching the semiconductormodules 66.

The cylinder 71 has the through-holes 78 which are formed near the endplate 63 and through which the wiring members 79 (see FIG. 2) pass toelectrically connect the stator 50 disposed outside the cylinder 71 andthe electrical components 62 arranged inside the cylinder 71. The wiringmembers 79, as illustrated in FIG. 2, connect with ends of the statorwinding 51 and the bus bars 76 c of the wiring module 76 using crimpingor welding techniques. The wiring members 79 are implemented by, forexample, bus bars whose joining surfaces are preferably flattened. Asingle through-hole 78 or a plurality of through-holes 78 are preferablyprovided. This embodiment has two through-holes 78. The use of the twothrough-holes 78 facilitates the ease with which terminals extendingfrom the two sets of the three-phase windings are connected by thewiring members 79, and is suitable for achieving multi-phase wireconnections.

The rotor 40 and the stator 50 are, as described already in FIG. 4,arranged within the housing 30 in this order in a radially inwarddirection. The inverter unit 60 is arranged radially inside the stator50. If a radius of the inner periphery of the housing 30 is defined asd, the rotor 40 and the stator 50 are located radially outside adistance of d×0.705 away from the center of rotation of the rotor 40. Ifa region located radially inside the inner periphery of the stator 50(i.e., the inner circumferential surface of the stator core 52) isdefined as a first region X1, and a region radially extending from theinner periphery of the stator 50 to the housing 30 is defined as asecond region X2, a cross-sectional area of the first region X1 is setgreater than that of the second region X2. As viewed in a region wherethe magnet unit 42 of the rotor 40 overlaps the stator winding 51, thevolume of the first region X1 is larger than that of the second regionX2.

The rotor 40 and the stator 50 are fabricated as a magnetic circuitcomponent assembly. In the housing 30, the first region X1 which islocated radially inside the inner peripheral surface of the magneticcircuit component assembly is larger in volume than the region X2 whichlies between the inner peripheral surface of the magnetic circuitcomponent assembly and the housing 30 in the radial direction.

Next, the structures of the rotor 40 and the stator 50 will be describedbelow in more detail.

Typical rotating electrical machines are known which are equipped with astator with an annular stator core which is made of a stack of steelplates and has a stator winding wound in a plurality of slots arrangedin a circumferential direction of the stator core. Specifically, thestator core has teeth extending in a radial direction thereof at a giveninterval away from a yoke. Each slot is formed between the two radiallyadjacent teeth. In each slot, a plurality of conductors are arranged inthe radial direction in the form of layers to form the stator winding.

However, the above described stator structure has a risk that when thestator winding is energized, an increase in magnetomotive force in thestator winding may result in magnetic saturation in the teeth of thestator core, thereby restricting torque density in the rotatingelectrical machine. In other words, rotational flux, as created by theenergization of the stator winding of the stator core, is thought of asconcentrating on the teeth, which has a risk of causing magneticsaturation.

Generally, IPM (Interior Permanent Magnet) rotors are known which have astructure in which permanent magnets are arranged on a d-axis of a d-qaxis coordinate system, and a rotor core is placed on a q-axis of thed-q axis coordinate system. Excitation of a stator winding near thed-axis will cause an excited magnetic flux to flow from a stator to arotor according to Fleming's rules. This causes magnetic saturation tooccur widely in the rotor core on the q-axis.

FIG. 7 is a torque diagrammatic view which demonstrates a relationshipbetween an ampere-turn (AT) representing a magnetomotive force createdby the stator winding and a torque density (Nm/L). A broken lineindicates characteristics of a typical IPM rotor-rotating electricalmachine. FIG. 7 shows that in the typical rotating electrical machine,an increase in magnetomotive force in the stator will cause magneticsaturation to occur at two places: the tooth between the slots and theq-axis rotor (i.e., the rotor core on the q-axis), thereby restrictingan increase in torque. In this way, a design value of the ampere-turn isrestricted at A1 in the typical rotating electrical machine.

In order to alleviate the above problem in this embodiment, the rotatingelectrical machine 10 is designed to have an additional structure, aswill be described below, in order to eliminate the restriction arisingfrom the magnetic saturation. Specifically, as a first measure, thestator 50 is designed to have a slot-less structure for eliminating themagnetic saturation occurring in the teeth of the stator core of thestator and also to use an SPM (Surface Permanent Magnet) rotor foreliminating the magnetic saturation occurring in a q-axis core of theIPM rotor. The first measure serves to eliminate the above described twoplaces where the magnetic saturation occurs, but however, may result ina decrease in torque in a low-current region (see an alternate long andshort dash line in FIG. 7). In order to alleviate this problem, as asecond measure, a polar anisotropic structure is employed to increase amagnetic path of magnets in the magnet unit 42 of the rotor 40 toenhance a magnetic force in order to increase a magnetic flux in the SPMrotor to minimize the torque decrease.

Additionally, as a third measure, a flattened conductor structure isemployed to decrease a thickness of conductors of the coil side portion53 of the stator winding 51 in the radial direction of the stator 50 forcompensating for the torque decrease. The above magnetic force-enhancedpolar anisotropic structure is thought of as resulting in a flow oflarge eddy current in the stator winding 51 facing the magnet unit 42.The third measure is, however, to employ the flattened conductorstructure in which the conductors have a decreased thickness in theradial direction, thereby minimizing the generation of the eddy currentin the stator winding 51 in the radial direction. In this way, the abovefirst to third structures are, as indicated by a solid line in FIG. 7,expected to greatly improve the torque characteristics usinghigh-magnetic force magnets and also alleviate a risk of generation of alarge eddy current resulting from the use of the high-magnetic forcemagnets.

Additionally, as a fourth measure, a magnet unit is employed which has apolar anisotropic structure to create a magnetic density distributionapproximating a sine wave. This increases a sine wave matchingpercentage using pulse control, as will be described later, to enhancethe torque and also results in a moderate change in magnetic flux,thereby minimizing an eddy-current loss (i.e., a copper loss caused byeddy current) as compared with radial magnets.

The sine wave matching percentage will be described below. The sine wavematching percentage may be derived by comparing a waveform, a cycle, anda peak value of a surface magnetic flux density distribution measured byactually moving a magnetic flux probe on a surface of a magnet withthose of a sine wave. The since wave matching percentage is given by apercentage of an amplitude of a primary waveform that is a waveform of afundamental wave in a rotating electrical machine to that of theactually measured waveform, that is, an amplitude of the sum of thefundamental wave and a harmonic component. An increase in the sine wavematching percentage will cause the waveform in the surface magnetic fluxdensity distribution to approach the waveform of the sine wave. When anelectrical current of a primary sine wave is delivered by an inverter toa rotating electrical machine equipped with magnets having an improvedsine wave matching percentage, it will cause a large degree of torque tobe produced, combined with the fact that the waveform in the surfacemagnetic flux density distribution of the magnet is close to thewaveform of a sine wave. The surface magnetic flux density distributionmay alternatively be derived using electromagnetic analysis according toMaxwell's equations.

As a fifth measure, the stator winding 51 is designed to have aconductor strand structure made of a bundle of wires. In the conductorstrand structure of the stator winding 51, the wires are connectedparallel to each other, thus enabling a high current or large amount ofcurrent to flow in the stator winding 51 and also minimizing an eddycurrent occurring in the conductors widened in the circumferentialdirection of the stator 50 more effectively than the third measure inwhich the conductors are flattened in the radial direction because eachof the wires has a decreased transverse sectional area. The use of thebundle of the wires will cancel an eddy current arising from magneticflux occurring according to Ampere's circuital law in response to themagnetomotive force produced by the conductors.

The use of the fourth and fifth measures minimizes the eddy-current lossresulting from the high magnetic force produced by the high-magneticforce magnets provided by the second measure and also enhance thetorque.

The slot-less structure of the stator 50, the flattened conductorstructure of the stator winding 51, and the polar anisotropic structureof the magnet unit 42 will be described below. The slot-less structureof the stator 50 and the flattened conductor structure of the statorwinding 51 will first be discussed. FIG. 8 is a transverse sectionalview illustrating the rotor 40 and the stator 50. FIG. 9 is a partiallyenlarged view illustrating the rotor 40 and the stator 50 in FIG. 8.FIG. 10 is a transverse sectional view of the stator 50 taken along theline X-X in FIG. 11. FIG. 11 is a longitudinal sectional view of thestator 50. FIG. 12 is a perspective view of the stator winding 51. FIGS.8 and 9 indicate directions of magnetization of magnets of the magnetunit 42 using arrows.

The stator core 52 is, as clearly illustrated in FIGS. 8 to 11, of acylindrical shape and made of a plurality of magnetic steel platesstacked in the axial direction of the stator core 52 to have a giventhickness in a radial direction of the stator core 52. The statorwinding 51 is mounted on the outer periphery of the stator core 52 whichfaces the rotor 40. The outer peripheral surface of the stator core 52facing the rotor 40 serves as a conductor mounting portion (i.e., aconductor area). The outer peripheral surface of the stator core 52 isshaped as a curved surface without any irregularities. A plurality ofconductor groups 81 are arranged on the outer peripheral surface of thestator core 52 at given intervals away from each other in thecircumferential direction of the stator core 52. The stator core 52functions as a back yoke that is a portion of a magnetic circuit workingto rotate the rotor 40. The stator 50 is designed to have a structure inwhich a tooth (i.e., a core) made of a soft magnetic material is notdisposed between a respective two of the conductor groups 81 arrangedadjacent each other in the circumferential direction (i.e., theslot-less structure). In this embodiment, a resin material of thesealing member 57 is disposed in the space or gap 56 between arespective adjacent two of the conductor groups 81. In other words, thestator 50 has a conductor-to-conductor member which is disposed betweenthe conductor groups 81 arranged adjacent each other in thecircumferential direction of the stator 50 and made of a non-magneticmaterial. The conductor-to-conductor members serve as the sealingmembers 57. Before the sealing members 57 are placed to seal the gaps56, the conductor groups 81 are arranged in the circumferentialdirection radially outside the stator core 52 at a given interval awayfrom each other through the gaps 56 that are conductor-to-conductorregions. This makes up the slot-less structure of the stator 50. Inother words, each of the conductor groups 81 is, as described later indetail, made of two conductors 82. An interval between a respective twoof the conductor groups 81 arranged adjacent each other in thecircumferential direction of the stator 50 is occupied only by anon-magnetic material. The non-magnetic material, as referred to herein,includes a non-magnetic gas, such as air, or a non-magnetic liquid. Inthe following discussion, the sealing members 57 will also be referredto as conductor-to-conductor members.

The structure, as referred to herein, in which the teeth arerespectively disposed between the conductor groups 81 arrayed in thecircumferential direction means that each of the teeth has a giventhickness in the radial direction and a given width in thecircumferential direction of the stator 50, so that a portion of themagnetic circuit, that is, a magnet magnetic path lies between theadjacent conductor groups 81. In contrast, the structure in which notooth lies between the adjacent conductor groups 81 means that there isno magnetic circuit between the adjacent conductor groups 81.

The stator winding (i.e., the armature winding) 51, as illustrated inFIG. 10, has a given thickness T2 (which will also be referred to belowas a first dimension) and a width W2 (which will also be referred tobelow as a second dimension). The thickness T2 is given by a minimumdistance between an outer side surface and an inner side surface of thestator winding 51 which are opposed to each other in the radialdirection of the stator 50. The width W2 is given by a dimension of aportion of the stator winding 51 which functions as one of multiplephases (i.e., the U-phase, the V-phase, the W-phase, the X-phase, theY-phase, and the Z-phase in this embodiment) of the stator winding 51 inthe circumferential direction. Specifically, in a case where the twoconductor groups 81 arranged adjacent each other in the circumferentialdirection in FIG. 10 serve as one of the three phases, for example, theU-phase winding, a distance between circumferentially outermost ends ofthe two circumferentially adjacent conductor groups 81 is the width W2.The thickness T2 is smaller than the width W2.

The thickness T2 is preferably set smaller than the sum of widths of thetwo conductor groups 81 within the width W2. If the stator winding 51(more specifically, the conductor 82) is designed to have a truecircular transverse section, an oval transverse section, or a polygonaltransverse section, the cross section of the conductor 82 taken in theradial direction of the stator 50 may be shaped to have a maximumdimension W12 in the radial direction of the stator 50 and a maximumdimension W11 in the circumferential direction of the stator 50.

The stator winding 51 is, as can be seen in FIGS. 10 and 11, sealed bythe sealing members 57 which are formed by a synthetic resin mold.Specifically, the stator winding 51 and the stator core 52 are put in amould together when the sealing members 57 are moulded by the resin. Theresin may be considered as a non-magnetic material or an equivalentthereof whose Bs (saturation magnetic flux density) is zero.

As a transverse section is viewed in FIG. 10, the sealing members 57 areprovided by placing synthetic resin in the gaps 56 between the conductorgroups 81. The sealing members 57 serve as insulators arranged betweenthe conductor groups 81. In other words, each of the sealing members 57functions as an insulator in one of the gaps 56. The sealing members 57occupy a region which is located radially outside the stator core 52,and includes all the conductor groups 81, in other words, which isdefined to have a dimension larger than that of each of the conductorgroups 81 in the radial direction.

As a longitudinal section is viewed in FIG. 11, the sealing members 57lie to occupy a region including the turns 84 of the stator winding 51.Radially inside the stator winding 51, the sealing members 57 lie in aregion including at least a portion of the axially opposed ends of thestator core 52. In this case, the stator winding 51 is fully sealed bythe resin except for the ends of each phase winding, i.e., terminalsjoined to the inverter circuits.

The structure in which the sealing members 57 are disposed in the regionincluding the ends of the stator core 52 enables the sealing members 57to compress the stack of the steel plates of the stator core 52 inwardlyin the axial direction. In other words, the sealing members 57 work tofirmly retain the stack of the steel plates of the stator core 52. Inthis embodiment, the inner peripheral surface of the stator core 52 isnot sealed using resin, but however, the whole of the stator core 52including the inner peripheral surface may be sealed using resin.

In a case where the rotating electrical machine 10 is used as a powersource for a vehicle, the sealing members 57 are preferably made of ahigh heat-resistance fluororesin, epoxy resin, PPS resin, PEEK resin,LCP resin, silicon resin, PAI resin, or PI resin. In terms of a linearcoefficient expansion to minimize breakage of the sealing members 57 dueto an expansion difference, the sealing members 57 are preferably madeof the same material as that of an outer film of the conductors of thestator winding 51. The silicon resin whose linear coefficient expansionis twice or more those of other resins is preferably excluded from thematerial of the sealing members 57. In a case of electrical products,such as electric vehicles equipped with no combustion engine, PPO resin,phenol resin, or FRP resin which resists 180° C. may be used, except infields where an ambient temperature of the rotating electrical machineis expected to be not higher than 100° C.

The degree of torque outputted by the rotating electrical machine 10 isusually proportional to the degree of magnetic flux. In a case where astator core is equipped with teeth, a maximum amount of magnetic flux inthe stator core is restricted depending upon the saturation magneticflux density in the teeth, while in a case where the stator core is notequipped with teeth, the maximum amount of magnetic flux in the statorcore is not restricted. Such a structure is, therefore, useful forincreasing an amount of electrical current delivered to the statorwinding 51 to increase the degree of torque produced by the rotatingelectrical machine 10.

This embodiment employs the slot-less structure in which the stator 50is not equipped with teeth, thereby resulting in a decrease ininductance of the stator 50. Specifically, a stator of a typicalrotating electrical machine in which conductors are disposed in slotsisolated by teeth from each other has an inductance of approximately 1mH, while the stator 50 in this embodiment has a decreased inductance of5 to 60 pH. The rotating electrical machine 10 in this embodiment is ofan outer rotor type, but has a decreased inductance of the stator 50 todecrease a mechanical time constant Tm. In other words, the rotatingelectrical machine 10 is capable of outputting a high degree of torqueand designed to have a decreased value of the mechanical time constantTm. If inertia is defined as J, inductance is defined as L, torqueconstant is defined as Kt, and back electromotive force constant isdefined as Ke, the mechanical time constant Tm is calculated accordingto the equation of Tm=(J×L)/(Kt×Ke). This shows that a decrease ininductance L will result in a decrease in mechanical time constant Tm.

Each of the conductor groups 81 arranged radially outside the statorcore 52 is made of a plurality of conductors 82 whose transverse sectionis of a flattened rectangular shape and which are disposed on oneanother in the radial direction of the stator core 52. Each of theconductors 82 is oriented to have a transverse section meeting arelation of radial dimension<circumferential dimension. This causes eachof the conductor groups 81 to be thin in the radial direction. Aconductive region of the conductor group 81 also extends inside a regionoccupied by teeth of a typical stator. This creates a flattenedconductive region structure in which a sectional area of each of theconductors 82 is increased in the circumferential direction, therebyalleviating a risk that the amount of thermal energy may be increased bya decrease in sectional area of a conductor arising from flattening ofthe conductor. A structure in which a plurality of conductors arearranged in the circumferential direction and connected in parallel toeach other is usually subjected to a decrease in sectional area of theconductors by a thickness of a coated layer of the conductors, buthowever, has beneficial advantages obtained for the same reasons asdescribed above. In the following discussion, each of the conductorgroups 81 or each of the conductors 82 will also be referred to as aconductive member.

The stator 50 in this embodiment is, as described already, designed tohave no slots, thereby enabling the stator winding 51 to be designed tohave a conductive region of an entire circumferential portion of thestator 50 which is larger in size than a non-conductive regionunoccupied by the stator winding 51 in the stator 50. In typicalrotating electrical machines for vehicles, a ratio of the conductiveregion/the non-conductive region is usually one or less. In contrast,this embodiment has the conductor groups 81 arranged to have theconductive region substantially identical in size with or larger in sizethan the non-conductive region. If the conductor region, as illustratedin FIG. 10, occupied by the conductor 82 (i.e., the straight section 83which will be described later in detail) in the circumferentialdirection is defined as WA, and a conductor-to-conductor region that isan interval between a respective adjacent two of the conductors 82 isdefined as WB, the conductor region WA is larger in size than theconductor-to-conductor region WB in the circumferential direction.

The conductor group 81 of the stator winding 51 has a thickness in theradial direction thereof which is smaller than a circumferential widthof a portion of the stator winding 51 which lies in a region of onemagnetic pole and serves as one of the phases of the stator winding 51.In the structure in which each of the conductor groups 81 is made up ofthe two conductors 82 stacked in the form of two layers lying on eachother in the radial direction, and the two conductor groups 81 arearranged in the circumferential direction within a region of onemagnetic pole for each phase, a relation of Tc×2<Wc×2 is met where Tc isthe thickness of each of the conductors 82 in the radial direction, andWc is the width of each of the conductors 82 in the circumferentialdirection. In another structure in which each of the conductor groups 81is made up of the two conductors 82, and each of the conductor groups 81lies within the region of one magnetic pole for each phase, a relationof Tc×2<Wc is preferably met. In other words, in the stator winding 51which is designed to have conductor portions (i.e., the conductor groups81) arranged at a given interval away from each other in thecircumferential direction, the thickness of each conductor portion(i.e., the conductor group 81) in the radial direction is set smallerthan the width of a portion of the stator winding 51 lying in the regionof one magnetic pole for each phase in the circumferential direction.

In other words, each of the conductors 82 is preferably shaped to havethe thickness Tc in the radial direction which is smaller than the widthWc in the circumferential direction. The thickness 2Tc of each of theconductor groups 81 each made of a stack of the two conductors 82 in theradial direction is preferably smaller than the width Wc of each of theconductor groups 81 in the circumferential direction.

The degree of torque produced by the rotating electrical machine 10 issubstantially inversely proportional to the thickness of the stator core52 in the radial direction. The conductor groups 81 arranged radiallyoutside the stator core 52 are, as described above, designed to have thethickness decreased in the radial direction. This design is useful inincreasing the degree of torque outputted by the rotating electricalmachine 10. This is because a distance between the magnet unit 42 of therotor 40 and the stator core 52 (i.e., a distance in which there is noiron) may be decreased to decrease the magnetic resistance. This enablesinterlinkage magnetic flux in the stator core 52 produced by thepermanent magnets to be increased to enhance the torque.

The decrease in thickness of the conductor groups 81 facilitates theease with which a magnetic flux leaking from the conductor groups 81 iscollected in the stator core 52, thereby preventing the magnetic fluxfrom leaking outside the stator core 52 without being used for enhancingthe torque. This avoids a drop in magnetic force arising from theleakage of the magnetic flux and increases the interlinkage magneticflux in the stator core 52 produced by the permanent magnets, therebyenhancing the torque.

Each of the conductors 82 is made of a coated conductor formed bycovering the surface of the conductor body 82 a with the coating 82 b.The conductors 82 stacked on one another in the radial direction are,therefore, insulated from each other. Similarly, the conductors 82 areinsulated from the stator core 52. The insulating coating 82 b may be acoating of each wire 86, as will be described later in detail, in a casewhere each wire 86 is made of wire with a self-bonded coating or may bemade by an additional insulator disposed on a coating of each wire 86.Each phase winding made of the conductors 82 is insulated by the coating82 b except an exposed portion thereof for joining purposes. The exposedportion includes, for example, an input or an output terminal or aneutral point in a case of a star connection. The conductor groups 81arranged adjacent each other in the radial direction are firmly adheredto each other using resin or self-bonding coated wire, therebyminimizing a risk of insulation breakdown, mechanical vibration, ornoise caused by rubbing of the conductors 82.

In this embodiment, the conductor body 82 a is made of a collection of aplurality of wires 86. Specifically, the conductor body 82 a is, as canbe seen in FIG. 13, made of a strand of the twisted wires 86. Each ofthe wires 86 is, as can be seen in FIG. 14, made of a bundle of aplurality of thin conductive fibers 87. For instance, each of the wires86 is made of a complex of CNT (carbon nanotube) fibers. The CNT fibersinclude boron-containing microfibers in which at least a portion ofcarbon is substituted with boron. Instead of the CNT fibers that arecarbon-based microfibers, vapor grown carbon fiber (VGCF) may be used,but however, CNT fiber is preferable. The surface of the wire 86 iscovered with a layer of insulating polymer, such as enamel. The surfaceof the wire 86 is preferably covered with an enamel coating, such aspolyimide coating or amide-imide coating.

The conductors 82 constitute n-phase windings of the stator winding 51.The wires 86 of each of the conductors 82 (i.e., the conductor body 82a) are placed in contact with each other. Each of the conductors 82 hasone of more portions which are formed by twisting the wires 86 anddefine one or more portions of a corresponding one of thephase-windings. A resistance value between the twisted wires 86 islarger than that of each of the wires 86. In other words, the respectiveadjacent two wires 86 have a first electrical resistivity in a directionin which the wires 86 are arranged adjacent each other. Each of thewires 86 has a second electrical resistivity in a lengthwise directionof the wire 86. The first electrical resistivity is larger than thesecond electrical resistivity. Each of the conductors 82 may be made ofan assembly of wires, i.e., the twisted wires 86 covered with insulatingmembers whose first electrical resistivity is very high. The conductorbody 82 a of each of the conductors 82 is made of a strand of thetwisted wires 86.

The conductor body 82 a is, as described above, made of the twistedwires 86, thereby reducing an eddy current created in each of the wires86, which reduces an eddy current in the conductor body 82 a. Each ofthe wires 86 is twisted, thereby causing each of the wires 86 to haveportions where directions of applied magnetic field are opposite eachother, which cancels a back electromotive force. This results in areduction in the eddy current. Particularly, each of the wires 86 ismade of the conductive fibers 87, thereby enabling the conductive fibers87 to be thin and also enabling the number of times the conductivefibers 87 are twisted to be increased, which enhances the reduction ineddy current.

How to insulate the wires 86 from each other is not limited to the abovedescribed use of the polymer insulating layer, but the contactresistance may be used to resist a flow of current between the wires 86.In other words, the above beneficial advantage is obtained by adifference in potential arising from a difference between the resistancebetween the twisted wires 86 and the resistance of each of the wires 86as long as the resistance between the wires 86 is larger than that ofeach of the wires 86. For instance, the contact resistance may beincreased by using production equipment for the wires 86 and productionequipment for the stator 50 (i.e., an armature) of the rotatingelectrical machine 10 as discrete devices to cause the wires 86 to beoxidized during a transport time or a work interval.

Each of the conductors 82 is, as described above, of a low-profile orflattened rectangular shape in cross section. The more than oneconductors 82 are arranged in the radial direction. Each of theconductors 82 is made of a strand of the wires 86 each of which isformed by a self-bonding coating wire equipped with, for example, afusing or bonding layer or an insulating layer and which are twistedwith the bonding layers fused together. Each of the conductors 82 mayalternatively be made by forming twisted wires with no bonding layer ortwisted self-bonding coating wires into a desired shape using syntheticresin. The insulating coating 82 b of each of the conductors 82 may havea thickness of 80 μm to 100 μm which is larger than that of a coating oftypical wire (i.e., 5 μm to 40 μm). In this case, a required degree ofinsulation between the conductors 82 is achieved even if no insulatingsheet is interposed between the conductors 82.

It is also advisable that the insulating coating 82 b be higher indegree of insulation than the insulating layer of the wire 86 to achieveinsulation between the phase windings. For instance, the polymerinsulating layer of the wire 86 has a thickness of, for example, 5 μm.In this case, the thickness of the insulating coating 82 b of theconductor 82 is preferably selected to be 80 μm to 100 μm to achieve theinsulation between the phase windings.

Each of the conductors 82 may alternatively be made of a bundle of theuntwisted wires 86. In brief, each of the conductors 82 may be made of abundle of the wires 86 whose entire lengths are twisted, whose portionsare twisted, or whose entire lengths are untwisted. Each of theconductors 82 constituting the conductor portion is, as described above,made of a bundle of the wires 86. The resistance between the wires 86 islarger than that of each of the wires 86.

The conductors 82 are each bent and arranged in a given pattern in thecircumferential direction of the stator winding 51, thereby forming thephase-windings of the stator winding 51. The stator winding 51, asillustrated in FIG. 12, includes the coil side portion 53 and the coilends 54 and 55. The conductors 82 have the straight sections 83 whichextend straight in the axial direction of the stator winding 51 and formthe coil side portion 53. The conductors 82 have the turns 84 which arearranged outside the coil side portion 53 in the axial direction andform the coil ends 54 and 55. Each of the conductor 82 is made of awave-shaped string of conductor formed by alternately arranging thestraight sections 83 and the turns 84. The straight sections 83 arearranged to face the magnet unit 42 in the radial direction. Thestraight sections 83 are arranged at a given interval away from eachother and joined together using the turns 84 located outside the magnetunit 42 in the axial direction. The straight sections 83 correspond to amagnet facing portion.

In this embodiment, the stator winding 51 is shaped in the form of anannular distributed winding. In the coil side portion 53, the straightsections 83 are arranged at an interval away from each other whichcorresponds to each pole pair of the magnet unit 42 for each phase. Ineach of the coil ends 54 and 55, the straight sections 83 for each phaseare joined together by the turn 84 which is of a V-shape. The straightsections 83 which are paired for each pole pair are opposite to eachother in a direction of flow of electrical current. A respective two ofthe straight sections 83 which are joined together by each of the turns84 are different between the coil end 54 and the coil end 55. The jointsof the straight sections 83 by the turns 84 are arranged in thecircumferential direction on each of the coil ends 54 and 55 to completethe stator winding in a hollow cylindrical shape.

More specifically, the stator winding 51 is made up of two pairs of theconductors 82 for each phase. The stator winding 51 is equipped with afirst three-phase winding set including the U-phase winding, the V-phasewinding, and the W-phase winding and a second three-phase phase windingset including the X-phase winding, the Y-phase winding, and the Z-phasewinding. The first three-phase phase winding set and the secondthree-phase winding set are arranged adjacent each other in the radialdirection in the form of two layers. If the number of phases of thestator winding 51 is defined as S (i.e., 6 in this embodiment), thenumber of the conductors 82 for each phase is defined as m, 2×S×m=2Smconductors 82 are used for each pole pair in the stator winding 51. Therotating electrical machine in this embodiment is designed so that thenumber of phases S is 6, the number m is 4, and 8 pole pairs are used.6×4×8=192 conductors 82 are arranged in the circumferential direction ofthe stator core 52.

The stator winding 51 in FIG. 12 is designed to have the coil sideportion 53 which has the straight sections 82 arranged in the form oftwo overlapping layers disposed adjacent each other in the radialdirection. Each of the coil ends 54 and 55 has a respective two of theturns 84 which extend from the radially overlapping straight sections 82in opposite circumferential directions. In other words, the conductors82 arranged adjacent each other in the radial direction are opposite toeach other in direction in which the turns 84 extend except for ends ofthe stator winding 51.

A winding structure of the conductors 82 of the stator winding 51 willbe described below in detail. In this embodiment, the conductors 82formed in the shape of a wave winding are arranged in the form of aplurality of layers (e.g., two layers) disposed adjacent or overlappingeach other in the radial direction. FIGS. 15(a) and 15(b) illustrate thelayout of the conductors 82 which form the n^(th) layer. FIG. 15(a)shows the configurations of the conductor 82, as the side of the statorwinding 51 is viewed. FIG. 15(b) shows the configurations of theconductors 82 as viewed in the axial direction of the stator winding 51.In FIGS. 15(a) and 15(b), locations of the conductor groups 81 areindicated by symbols D1, D2, D3, . . . , and D9. For the sake ofsimplicity of disclosure, FIGS. 15(a) and 15(b) show only threeconductors 82 which will be referred to herein as the first conductor82_A, the second conductor 82_B, and the third conductor 82_C.

The conductors 82_A to 82_C have the straight sections 83 arranged at alocation of the n^(th) layer, in other words, at the same position inthe circumferential direction. Every two of the straight sections 82which are arranged at 6 pitches (corresponding to 3×m pairs) away fromeach other are joined together by one of the turns 84. In other words,in the conductors 82_A to 82_C, an outermost two of the seven straightsections 83 arranged in the circumferential direction of the statorwinding 51 on the same circle defined about the center of the rotor 40are joined together using one of the turns 84. For instance, in thefirst conductor 82_A, the straight sections 83 placed at the locationsD1 and D7 are joined together by the inverse V-shaped turn 84. Theconductors 82_B and 82_C are arranged at an interval equivalent to aninterval between a respective adjacent two of the straight sections 83away from each other in the circumferential direction at the location ofthe n^(th) layer. In this layout, the conductors 82_A to 82_C are placedat a location of the same layer, thereby resulting in a risk that theturns 84 thereof may physically interfere with each other. In order toalleviate such a risk, each of the turns 84 of the conductors 82_A to82_C in this embodiment is shaped to have an interference avoidingportion formed by offsetting a portion of the turn 84 in the radialdirection.

Specifically, the turn 84 of each of the conductors 82_A to 82_Cincludes the slant portion 84 a, the head portion 84 b, the slantportion 84 c, and the return portion 84 d. The slant portion 84 aextends in the circumferential direction of the same circle (which willalso be referred to as a first circle). The head portion 84 extends fromthe slant portion 84 a radially inside the first circle (i.e., upward inFIG. 15(b)) to reach another circle (which will also be referred to as asecond circle). The slant portion 84 c extends in the circumferentialdirection of the second circle. The return portion 84 d returns from thesecond circle back to the first circle. The head portion 84 b, the slantportion 84 c, and the return portion 84 d define the interferenceavoiding portion. The slant portion 84 c may be arranged radiallyoutside the slant portion 84 a.

In other words, each of the conductors 82_A to 82_C has the turn 84shaped to have the slant portion 84 a and the slant portion 84 c whichare arranged on opposite sides of the head portion 84 b at the center inthe circumferential direction. The locations of the slant portions 84 aand 84 b are different from each other in the radial direction (i.e., adirection perpendicular to the drawing of FIG. 15(a) or a verticaldirection in FIG. 15(b)). For instance, the turn 84 of the firstconductor 82_A is shaped to extend from the location D1 on the n^(th)layer in the circumferential direction, be bent at the head portion 84 bthat is the center of the circumferential length of the turn 84 in theradial direction (e.g., radially inwardly), be bent again in thecircumferential direction, extend again in the circumferentialdirection, and then be bent at the return portion 84 d in the radialdirection (e.g., radially outwardly) to reach the location D7 on then^(th) layer.

With the above arrangements, the slant portions 84 a of the conductors82_A to 82_C are arranged vertically or downward in the order of thefirst conductor 82_A, the second conductor 82_B, and the third conductor82_C. The head portions 84 b change the order of the locations of theconductors 82_A to 82_C in the vertical direction, so that the slantportions 84 c are arranged vertically or downward in the order of thethird conductor 82_3, the second conductor 82_B, and the first conductor82_A. This layout achieves an arrangement of the conductors 82_A to 82_Cin the circumferential direction without any physical interference witheach other.

In the structure wherein the conductors 82 are laid to overlap eachother in the radial direction to form the conductor group 81, the turns84 leading to a radially innermost one and a radially outermost one ofthe straight sections 83 forming the two or more layers are preferablylocated radially outside the straight sections 83. In a case where theconductors 83 forming the two or more layers are bent in the same radialdirection near boundaries between ends of the turns 84 and the straightsections 83, the conductors 83 are preferably shaped not to deterioratethe insulation therebetween due to physical interference of theconductors 83 with each other.

In the example of FIGS. 15(a) and 15(b), the conductors 82 laid on eachother in the radial direction are bent radially at the return portions84 d of the turns 84 at the location D7 to D9. It is advisable that theconductor 82 of the n^(th) layer and the conductor 82 of the n+1^(th)layer be bent, as illustrated in FIG. 16, at radii of curvaturedifferent from each other. Specifically, the radius of curvature R1 ofthe conductor 82 of the n^(th) layer is preferably selected to besmaller than the radius of curvature R2 of the conductor 82 of then+1^(th) layer.

Additionally, radial displacements of the conductor 82 of the n^(th)layer and the conductor 82 of the n+1^(th) layer are preferably selectedto be different from each other. If the amount of radial displacement ofthe conductor 82 of the n^(th) layer is defined as S1, and the amount ofradial displacement of the conductor 82 of the n+1^(th) layer locatedradially outside the n^(th) layer defined as S2, the amount of radialdisplacement S1 is preferably selected to be greater than the amount ofradial displacement S2.

The above layout of the conductors 82 eliminates the risk ofinterference with each other, thereby ensuring a required degree ofinsulation between the conductors 82 even when the conductors 82 laid oneach other in the radial direction are bent in the same direction.

The structure of the magnet unit 42 of the rotor 40 will be describedbelow. In this embodiment, the magnet unit 42 is made of permanentmagnets in which a remanent flux density Br=1.0 T, and an intrinsiccoercive force Hcj=400 kA/m. The permanent magnets used in thisembodiment are implemented by sintered magnets formed by sinteringgrains of magnetic material and compacting them into a given shape andhave the following specifications. The intrinsic coercive force Hcj on aJ-H curve is 400 kA/m or more. The remanent flux density Br on the J-Hcurve is 1.0 T or more. Magnets designed so that when 5,000 to 10,000 ATis applied thereto by phase-to-phase excitation, a magnetic distancebetween paired poles, i.e., between a N-pole and an S-pole, in otherwords, of a path in which a magnetic flux flows between the N-pole andthe S-pole, a portion lying in the magnet has a length of 25 mm may beused to meet a relation of Hcj=10000A without becoming demagnetized.

In other words, the magnet unit 42 is engineered so that a saturationmagnetic flux density Js is 1.2 T or more, a grain size is 10 μm orless, and a relation of Js×a≥1.0 T is met where a is an orientationratio.

The magnet unit 42 will be additionally described below. The magnet unit42 (i.e., magnets) has a feature that Js meets a relation of 2.15T≥Js≥1.2 T. In other words, magnets used in the magnet unit 42 may beFeNi magnets having NdFe11TiN, Nd2Fe14B, Sm2Fe17N3, or L10 crystals.Note that samarium-cobalt magnets, such as SmCo5, FePt, Dy2Fe14B, orCoPt magnets can not be used. When magnets in which high Jscharacteristics of neodymium are slightly lost, but a high degree ofcoercive force of Dy is ensured using the heavy rare earth dysprosium,like in isomorphous compounds, such as Dy2Fe14B and Nd2Fe14B, sometimesmeets a relation of 2.15 T≥Js≥1.2 T, they may be used in the magnet unit42. Such a type of magnet will also be referred to herein as[Nd1−xDyx]2Fe14B]. Further, a magnet contacting different types ofcompositions, in other words, a magnet made from two or more types ofmaterials, such as FeNi and Sm2Fe17N3, may be used to meet a relation of2.15 T≥Js≥1.2 T. A mixed magnet made by adding a small amount of, forexample, Dy2Fe14B in which Js<1 T to an Nd2Fe14B magnet in which Js=1.6T, meaning that Js is sufficient to enhance the coercive force, may alsobe used to meet a relation of 2.15 T≥Js≥1.2 T.

In use of the rotating electrical machine at a temperature outside atemperature range of human activities which is higher than, for example,60° C. exceeding temperatures of deserts, for example, within apassenger compartment of a vehicle where the temperature may rise to 80°C. in summer, the magnet preferably contains FeNi or Sm2Fe17N3components which are less dependent on temperature. This is becausemotor characteristics are greatly changed by temperature-dependentfactors thereof in motor operations within a range of approximately −40°which is within a range experienced by societies in Northern Europe to60° C. or more experienced in desert region or at 180 to 240° C. that isa heat resistance temperature of the enamel coating, which leads to adifficulty in achieving a required control operation using the samemotor driver. The use of FeNi containing the above described L10crystals or Sm2Fe17N3 magnets will result in a decrease in load on themotor driver because characteristics thereof have temperature-dependentfactors lower than half that of Nd2Fe14B magnets.

Additionally, the magnet unit 42 is engineered to use the abovedescribed magnet mixing so that a particle size of fine powder beforebeing magnetically oriented is lower than or equal to 10 μm and higherthan or equal to a size of single-domain particles. The coercive forceof a magnet is usually increased by decreasing the size of poweredparticles thereof to a few hundred nm. In recent years, smallestpossible particles have been used. If the particles of the magnet aretoo small, the BHmax (i.e., the maximum energy product) of the magnetwill be decreased due to oxidization thereof. It is, thus, preferablethat the particle size of the magnet is higher than or equal to the sizeof the single-domain particles. The particle size being only up to thesize of the single-domain particles is known to increase the coerciveforce of the magnet. The particle size, as referred to herein, refers tothe diameter or size of fine powdered particles in a magneticorientation operation in production processes of magnets.

Each of the first magnet 91 and the second magnet 92 of the magnet unit42 are made of sintered magnets formed by firing or heating magneticpowder at high temperatures and compacting it. The sintering is achievedso as to meet conditions where the saturation magnetization Js of themagnet unit 42 is 1.2 T (Tesla) or more, the particle size of the firstmagnet 91 and the second magnet 92 is 10 μm or less, and Js×a is higherthan or equal to 1.0 T (Tesla) where a is an orientation ratio. Each ofthe first magnet 91 and the second magnet 92 are also sintered to meetthe following conditions. By performing the magnetic orientation in themagnetic orientation operation in the production processes of the firstmagnet 91 and the second magnet 92, they have an orientation ratiodifferent to the definition of orientation of magnetic force in amagnetization operation for isotropic magnets. The magnet unit 42 inthis embodiment is designed to have the saturation magnetization Js morethan or equal to 1.2 T and the orientation ratio a of the first magnet91 and the second magnet 92 which is high to meet a relation ofJr≥Js×a≥1.0 T. The orientation ratio a, as referred to herein, isdefined in the following way. If each of the first magnet 91 and thesecond magnet 92 has six easy axes of magnetization, five of the easyaxes of magnetization are oriented in the same direction A10, and aremaining one of the easy axes of magnetization is oriented in thedirection B10 angled at 90 degrees to the direction A10, then a relationof a=⅚ is met. Alternatively, if each of the first magnet 91 and thesecond magnet 92 has six easy axes of magnetization, five of the easyaxes of magnetization are oriented in the same direction A10, and aremaining one of the easy axes of magnetization is oriented in thedirection B10 angled at 45 degrees to the direction A10, then a relationof a=(5+0.707)/6 is met since a component oriented in the direction A10is expressed by cos 45°=0.707. The first magnet 91 and the second magnet92 in this embodiment are, as described above, each made using sinteringtechniques, but however, they may be produced in another way as long asthe above conditions are satisfied. For instance, a method of forming anMQ3 magnet may be used.

In this embodiment, permanent magnets are used which are magneticallyoriented to control the easy axis of magnetization thereof, therebyenabling a magnetic circuit length within the magnets to be longer thanthat within typical linearly oriented magnets which produces a magneticflux density of 1.0 T or more. In other words, the magnetic circuitlength for one pole pair in the magnets in this embodiment may beachieved using magnets with a small volume. Additionally, a range ofreversible flux loss in the magnets is not lost when subjected to severehigh temperatures, as compared with use of typical linearly orientedmagnets. The inventors of this application have found thatcharacteristics similar to those of anisotropic magnets are obtainedeven using prior art magnets.

The easy axis of magnetization represents a crystal orientation in whicha crystal is easy to magnetize in a magnet. The orientation of the easyaxis of magnetization in the magnet, as referred to herein, is adirection in which an orientation ratio is 50% or more where theorientation ratio indicates the degree to which easy axes ofmagnetization of crystals are aligned with each other or a direction ofan average of magnetic orientations in the magnet.

The magnet unit 42 is, as clearly illustrated in FIGS. 8 and 9, of anannular shape and arranged inside the magnet holder 41 (specifically,radially inside the cylinder 43). The magnet unit 42 is equipped withthe first magnets 91 and the second magnets 92 which are each made of apolar anisotropic magnet. Each of the first magnets 91 and each of thesecond magnets 92 are different in magnetic polarity from each other.The first magnets 91 and the second magnets 92 are arranged alternatelyin the circumferential direction of the magnet unit 42. Each of thefirst magnets 91 is engineered to have a portion creating an N-pole nearthe stator winding 51. Each of the second magnets 92 is engineered tohave a portion creating an S-pole near the stator winding 51. The firstmagnets 91 and the second magnets 92 are each made of, for example, apermanent rare earth magnet, such as a neodymium magnet.

Each of the magnets 91 and 92 is engineered to have a direction ofmagnetization (which will also be referred to below as a magnetizationdirection) which extends in an annular shape in between a d-axis (i.e.,a direct-axis) and a q-axis (i.e., a quadrature-axis) in a known d-qcoordinate system where the d-axis represents the center of a magneticpole, and the q-axis represents a magnetic boundary between the N-poleand the S-pole, in other words, where a density of magnetic flux is zeroTesla. In each of the magnets 91 and 92, the magnetization direction isoriented in the radial direction of the annular magnet unit 42 close tothe d-axis and also oriented in the circumferential direction of theannular magnet unit 42 closer to the q-axis. This layout will also bedescribed below in detail. Each of the magnets 91 and 92, as can be seenin FIG. 9, includes a first portion 250 and two second portions 260arranged on opposite sides of the first portion 250 in thecircumferential direction of the magnet unit 42. The first portion 250is located closer to the d-axis than the second portions 260 are. Thesecond portions 260 are arranged closer to the q-axis than the firstportion 250 is. The direction in which the easy axis of magnetization300 extends in the first portion 250 is oriented more parallel to thed-axis than the direction in which the easy axis of magnetization 310extends in the second portions 260. To say it in a different way, theeasy axis of magnetization has a first portion lying in the firstportion 250 of each of the magnets 91 and 92 and second portions lyingin the second portions 260 of each of the magnets 91 and 92. The firstportion of the easy axis of magnetization extends more parallel to thed-axis than the second portions of the easy axis of magnetization do. Inother words, the magnet unit 42 is engineered so that an angle θ11 whichthe easy axis of magnetization 300 in the first portion 250 makes withthe d-axis is selected to be smaller than an angle θ12 which the easyaxis of magnetization 310 in the second portion 260 makes with theq-axis.

More specifically, if a direction from the stator 50 (i.e., an armature)toward the magnet unit 42 on the d-axis is defined to be positive, theangle θ11 represents an angle which the easy axis of magnetization 300makes with the d-axis. Similarly, if a direction from the stator 50(i.e., an armature) toward the magnet unit 42 on the q-axis is definedto be positive, the angle θ12 represents an angle which the easy axis ofmagnetization 310 makes with the q-axis. In this embodiment, each of theangle θ11 and the angle θ12 is set to be 90° or less. Each of the easyaxes of magnetization 300 and 310, as referred to herein, is defined inthe following way. If in each of the magnets 91 and 92, a first one ofthe easy axes of magnetization is oriented in a direction A11, and asecond one of the easy axes of magnetization is oriented in a directionB11, an absolute value of cosine of an angle θ which the direction A11and the direction B11 make with each other (i.e., |cos θ|) is defined asthe easy axis of magnetization 300 or the easy axis of magnetization310.

The magnets 91 are different in easy axis of magnetization from themagnets 92 in regions close to the d-axis and the q-axis. Specifically,in the region close to the d-axis, the direction of the easy axis ofmagnetization is oriented approximately parallel to the d-axis, while inthe region close to the q-axis, the direction of the easy axis ofmagnetization is oriented approximately perpendicular to the q-axis.Annular magnetic paths are created according to the directions of easyaxes of magnetization. In each of the magnets 91 and 92, the easy axisof magnetization in the region close to the d-axis may be orientedparallel to the d-axis, while the easy axis of magnetization in theregion close to the q-axis may be oriented perpendicular to the q-axis.

Each of the magnets 91 and 92 is shaped to have a first peripheralsurface facing the stator 50 (i.e., a lower surface viewed in FIG. 9which will also be referred to as a stator-side outer surface) and asecond peripheral surface facing the q-axis in the circumferentialdirection. The first and second peripheral surfaces function as magneticflux acting surfaces into and from which magnetic flux flows. Themagnetic paths are each created to extend between the magnetic fluxacting surfaces (i.e., between the stator-side outer surface and thesecond peripheral surface facing the q-axis).

In the magnet unit 42, a magnetic flux flows in an annular shape betweena respective adjacent two of the N-poles and the S-poles of the magnets91 and 92, so that each of the magnetic paths has an increased length,as compared with, for example, radial anisotropic magnets. Adistribution of the magnetic flux density will, therefore, exhibit ashape similar to a sine wave illustrated in FIG. 17. This facilitatesconcentration of magnetic flux around the center of the magnetic poleunlike a distribution of magnetic flux density of a radial anisotropicmagnet demonstrated in FIG. 18 as a comparative example, therebyenabling the degree of torque produced by the rotating electricalmachine 10 to be increased. It has also been found that the magnet unit42 in this embodiment has the distribution of the magnetic flux densitydistinct from that of a typical Halbach array magnet. In FIGS. 17 and18, a horizontal axis indicates the electrical angle, while a verticalaxis indicates the magnetic flux density. 90° on the horizontal axisrepresents the d-axis (i.e., the center of the magnetic pole). 0° and180° on the horizontal axis represent the q-axis.

Accordingly, the above described structure of each of the magnets 91 and92 functions to enhance the magnet magnetic flux thereof on the d-axisand reduce a change in magnetic flux near the q-axis. This enables themagnets 91 and 92 to be produced which have a smooth change in surfacemagnetic flux from the q-axis to the d-axis on each magnetic pole.

The sine wave matching percentage in the distribution of the magneticflux density is preferably set to, for example, 40% or more. Thisimproves the amount of magnetic flux around the center of a waveform ofthe distribution of the magnetic flux density as compared with aradially oriented magnet or a parallel oriented magnet in which the sinewave matching percentage is approximately 30%. By setting the sine wavematching percentage to be 60% or more, the amount of magnetic fluxaround the center of the waveform is improved, as compared with aconcentrated magnetic flux array, such as the Halbach array.

In the radial anisotropic magnet demonstrated in FIG. 18, the magneticflux density changes sharply near the q-axis. The more sharp the changein magnetic flux density, the more an eddy current generated in thestator winding 51 will increase. The magnetic flux close to the statorwinding 51 also sharply changes. In contrast, the distribution of themagnetic flux density in this embodiment has a waveform approximating asine wave. A change in magnetic flux density near the q-axis is,therefore, smaller than that in the radial anisotropic magnet near theq-axis. This minimizes the generation of the eddy current.

The magnet unit 42 creates a magnetic flux oriented perpendicular to themagnetic flux acting surface 280 close to the stator 50 near the d-axis(i.e., the center of the magnetic pole) in each of the magnets 91 and92. Such a magnetic flux extends in an arc-shape farther away from thed-axis as departing from the magnetic flux acting surface 280 close tothe stator 50. The more perpendicular to the magnetic flux actingsurface the magnetic flux extends, the stronger the magnetic flux is.The rotating electrical machine 10 in this embodiment is, as describedabove, designed to shape each of the conductor groups 81 to have adecreased thickness in the radial direction, so that the radial centerof each of the conductor groups 81 is located close to the magneticflux-acting surface of the magnet unit 42, thereby causing the strongmagnetic flux to be applied to the stator 50 from the rotor 40.

The stator 50 has the cylindrical stator core 52 arranged radiallyinside the stator winding 51, that is, on the opposite side of thestator winding 51 to the rotor 40. This causes the magnetic fluxextending from the magnetic flux-acting surface of each of the magnets91 and 92 to be attracted by the stator core 52, so that it circulatesthrough the magnetic path partially including the stator core 52. Thisenables the orientation of the magnetic flux and the magnetic path to beoptimized.

Steps to assemble the bearing unit 20, the housing 30, the rotor 40, thestator 50, and the inverter unit 60 illustrated in FIG. 5 will bedescribed below as a production method of the rotating electricalmachine 10. The inverter unit 60 is, as illustrated in FIG. 6, equippedwith the unit base 61 and the electrical components 62. Operationprocesses including installation processes for the unit base 61 and theelectrical components 62 will be explained. In the following discussion,an assembly of the stator 50 and the inverter unit 60 will be referredto as a first unit. An assembly of the bearing unit 20, the housing 30,and the rotor 40 will be referred to as a second unit.

The production processes include:

a first step of installing the electrical components 62 radially insidethe unit base 61;

a second step of installing the unit base 61 radially inside the stator50 to make the first unit;

a third step of inserting the attaching portion 44 of the rotor 40 intothe bearing unit 20 installed in the housing 30 to make the second unit;

a fourth step of installing the first unit radially inside the secondunit; and

a fifth step of fastening the housing 30 and the unit base 61 together.The order in which the above steps are performed is the first step→thesecond step→the third step→the fourth step→the fifth step.

In the above production method, the bearing unit 20, the housing 30, therotor 40, the stator 50, and the inverter unit 60 are assembled as aplurality of sub-assemblies, and the sub-assemblies are assembled,thereby facilitating handling thereof and achieving completion ofinspection of each sub-assembly. This enables an efficient assembly lineto be established and thus facilitates multi-product productionplanning.

In the first step, a high thermal conductivity material is applied oradhered to at least one of the radial inside of the unit base 61 and theradial outside of the electrical components 62. Subsequently, theelectrical components may be mounted on the unit base 61. This achievesefficient transfer of heat, as generated by the semiconductor modules66, to the unit base 61.

In the third step, an insertion operation for the rotor 40 may beachieved with the housing 30 and the rotor 40 arranged coaxially witheach other. Specifically, the housing 30 and the rotor 40 are assembledwhile sliding one of the housing 30 and the rotor 40 along a jig whichpositions the outer peripheral surface of the rotor 40 (i.e., the outerperipheral surface of the magnetic holder 41) or the inner peripheralsurface of the rotor 40 (i.e., the inner peripheral surface of themagnet unit 42) with respect to, for example, the inner peripheralsurface of the housing 30. This achieves the assembly of heavy-weightparts without exertion of unbalanced load to the bearing unit 20. Thisresults in improvement of reliability in operation of the bearing unit20.

In the fourth step, the first unit and the second unit may be installedwhile being placed coaxially with each other. Specifically, the firstunit and the second unit are installed while sliding one of the firstunit and the second unit along a jig which positions the innerperipheral surface of the unit base 61 with respect to, for example, theinner peripheral surfaces of the rotor 40 and the attaching portion 44.This achieves the installation of the first and second units without anyphysical interference therebetween within a small clearance between therotor 40 and the stator 50, thereby eliminating risks of defects causedby the installation, such as physical damage to the stator winding 51 ordamage to the permanent magnets.

The above steps may alternatively be scheduled as the second step→thethird step→the fourth step→the fifth step→the first step. In this order,the delicate electrical components 62 is finally installed, therebyminimizing stress on the electrical components in the installationprocesses.

The structure of a control system for controlling an operation of therotating electrical machine 10 will be described below. FIG. 19 is anelectrical circuit diagram of the control system for the rotatingelectrical machine 10. FIG. 20 is a functional block diagram whichillustrates control steps performed by the controller 110.

FIG. 19 illustrates two sets of three-phase windings 51 a and 51 b. Thethree-phase winding 51 a includes a U-phase winding, a V-phase winding,and a W-phase winding. The three-phase winding 51 b includes an X-phasewinding, a Y-phase winding, and a Z-phase winding. The first inverter101 and the second inverter 102 are provided as electrical powerconverters for the three-phase windings 51 a and 51 b, respectively. Theinverters 101 and 102 are made of bridge circuits with as many upper andlower arms as there are the phase-windings. The current delivered to thephase windings of the stator winding 51 is regulated by turning on oroff switches (i.e., semiconductor switches) mounted on the upper andlower arms.

The dc power supply 103 and the smoothing capacitor 104 are connectedparallel to the inverters 101 and 102. The dc power supply 103 is madeof, for example, a plurality of series-connected cells. The switches ofthe inverters 101 and 102 correspond to the semiconductor modules 66 inFIG. 1. The capacitor 104 corresponds to the capacitor module 68 in FIG.1.

The controller 110 is equipped with a microcomputer made of a CPU andmemories and works to perform control energization by turning on or offthe switches of the inverters 101 and 102 using several types ofmeasured information measured in the rotating electrical machine 10 orrequests for a motor mode or a generator mode of the rotating electricalmachine 10. The controller 110 corresponds to the control device 77shown in FIG. 6. The measured information about the rotating electricalmachine 10 includes, for example, an angular position (i.e., anelectrical angle) of the rotor 40 measured by an angular positionsensor, such as a resolver, a power supply voltage (i.e., voltageinputted into the inverters) measured by a voltage sensor, andelectrical current delivered to each of the phase-windings, as measuredby a current sensor. The controller 110 produces and outputs anoperation signal to operate each of the switches of the inverters 101and 102. A request for electrical power generation is a request fordriving the rotating electrical machine 10 in a regenerative mode, forexample, in a case where the rotating electrical machine 10 is used as apower source for a vehicle.

The first inverter 101 is equipped with a series-connected part made upof an upper arm switch Sp and a lower arm switch Sn for each of thethree-phase windings: the U-phase winding, the V-phase winding, and theW-phase winding. The upper arm switches Sp are connected athigh-potential terminals thereof to a positive terminal of the dc powersupply 103. The lower arm switches Sn are connected at low-potentialterminals thereof to a negative terminal (i.e., ground) of the dc powersupply 103. Intermediate joints of the upper arm switches Sp and thelower arm switches Sn are connected to ends of the U-phase winding, theV-phase winding, and the W-phase winding. The U-phase winding, theV-phase winding, and the W-phase winding are connected in the form of astar connection (i.e., Y-connection). The other ends of the U-phasewinding, the V-phase winding, and the W-phase winding are connected witheach other at a neutral point.

The second inverter 102 is, like the first inverter 101, equipped with aseries-connected part made up of an upper arm switch Sp and a lower armswitch Sn for each of the three-phase windings: the X-phase winding, theY-phase winding, and the Z-phase winding. The upper arm switches Sp areconnected at high-potential terminals thereof to the positive terminalof the dc power supply 103. The lower arm switches Sn are connected atlow-potential terminals thereof to the negative terminal (i.e., ground)of the dc power supply 103. Intermediate joints of the upper armswitches Sp and the lower arm switches Sn are connected to ends of theX-phase winding, the Y-phase winding, and the Z-phase winding. TheX-phase winding, the Y-phase winding, and the Z-phase winding areconnected in the form of a star connection (i.e., Y-connection). Theother ends of the X-phase winding, the Y-phase winding, and the Z-phasewinding are connected with each other at a neutral point.

FIG. 20 illustrates a current feedback control operation to controlelectrical currents delivered to the U-phase winding, the V-phasewinding, and the W-phase winding and a current feedback controloperation to control electrical currents delivered to the X-phasewinding, the Y-phase winding, and the Z-phase winding. The controloperation for the U-phase winding, the V-phase winding, and the W-phasewinding will first be discussed.

In FIG. 20, the current command determiner 111 uses a torque-dq map todetermine current command values for the d-axis and the q-axis using atorque command value in the motor mode of the rotating electricalmachine 10 (which will also be referred to as a motor-mode torquecommand value), a torque command value in the generator mode of therotating electrical machine 10 (which will be referred to as agenerator-mode torque command value), and an electrical angular velocityω derived by differentiating an electrical angle θ with respect to time.The current command determiner 111 is shared between the U-, V-, andW-phase windings and the X-, Y-, and W-phase windings. Thegenerator-mode torque command value is a regenerative torque commandvalue in a case where the rotating electrical machine 10 is used as apower source of a vehicle.

The d-q converter 112 works to convert currents (i.e., three phasecurrents), as measured by current sensors mounted for the respectivephase windings, into a d-axis current and a q-axis current that arecomponents in a two-dimensional rotating Cartesian coordinate system inwhich a d-axis is defined as a direction of an axis of a magnetic fieldor field direction.

The d-axis current feedback control device 113 determines a commandvoltage for the d-axis as a manipulated variable for bringing the d-axiscurrent into agreement with the current command value for the d-axis ina feedback mode. The q-axis current feedback control device 114determines a command voltage for the q-axis as a manipulated variablefor bringing the q-axis current into agreement with the current commandvalue for the q-axis in a feedback mode. The feedback control devices113 and 114 calculates the command voltage as a function of a deviationof each of the d-axis current and the q-axis current from acorresponding one of the current command values using PI feedbacktechniques.

The three-phase converter 115 works to convert the command values forthe d-axis and the q-axis into command values for the U-phase, V-phase,and W-phase windings. Each of the devices 111 to 115 is engineered as afeedback controller to perform a feedback control operation for afundamental current in the d-q transformation theory. The commandvoltages for the U-phase, V-phase, and W-phase windings are feedbackcontrol values.

The operation signal generator 116 uses the known triangle wave carriercomparison to produce operation signals for the first inverter 101 as afunction of the three-phase command voltages. Specifically, theoperation signal generator 116 works to produce switch operation signals(i.e., duty signals) for the upper and lower arms for the three-phasewindings (i.e., the U-, V-, and W-phase windings) under PWM controlbased on comparison of levels of signals derived by normalizing thethree-phase command voltages using the power supply voltage with a levelof a carrier signal, such as a triangle wave signal.

The same structure as described above is provided for the X-, Y-, andZ-phase windings. The d-q converter 122 works to convert currents (i.e.,three phase currents), as measured by current sensors mounted for therespective phase windings, into a d-axis current and a q-axis currentthat are components in the two-dimensional rotating Cartesian coordinatesystem in which the d-axis is defined as the direction of the axis ofthe magnetic field.

The d-axis current feedback control device 123 determines a commandvoltage for the d-axis. The q-axis current feedback control device 124determines a command voltage for the q-axis. The three-phase converter125 works to convert the command values for the d-axis and the q-axisinto command values for the X-phase, Y-phase, and Z-phase windings. Theoperation signal generator 126 produces operation signals for the secondinverter 102 as a function of the three-phase command voltages.Specifically, the operation signal generator 126 works to switchoperation signals (i.e., duty signals) for the upper and lower arms forthe three-phase windings (i.e., the X-, Y-, and Z-phase windings) basedon comparison of levels of signals derived by normalizing thethree-phase command voltages using the power supply voltage with a levelof a carrier signal, such as a triangle wave signal.

The driver 117 works to turn on or off the switches Sp and Sn in theinverters 101 and 102 in response to the switch operation signalsproduced by the operation signal generators 116 and 126.

Subsequently, a torque feedback control operation will be describedbelow. This operation is to increase an output of the rotatingelectrical machine 10 and reduce torque loss in the rotating electricalmachine 10, for example, in a high-speed and high-output range whereinoutput voltages from the inverters 101 and 102 rise. The controller 110selects one of the torque feedback control operation and the currentfeedback control operation and perform the selected one as a function ofan operating condition of the rotating electrical machine 10.

FIG. 21 shows the torque feedback control operation for the U-, V-, andW-phase windings and the torque feedback control operation for the X-,Y-, and Z-phase windings. In FIG. 21, the same reference numbers asemployed in FIG. 20 refer to the same parts, and explanation thereof indetail will be omitted here. The control operation for the U-, V-, andW-phase windings will be described first.

The voltage amplitude calculator 127 works to calculate a voltageamplitude command that is a command value of a degree of a voltagevector as a function of the motor-mode torque command value or thegenerator-mode torque command value for the rotating electrical machine10 and the electrical angular velocity ω derived by differentiating theelectrical angle θ with respect to time.

The torque calculator 128 a works to estimate a torque value in theU-phase, V-phase, or the W-phase as a function of the d-axis current andthe q-axis current converted by the d-q converter 112. The torquecalculator 128 a may be designed to calculate the voltage amplitudecommand using a map listing relations among the d-axis current, theq-axis current, and the voltage amplitude command.

The torque feedback controller 129 a calculates a voltage phase commandthat is a command value for a phase of the voltage vector as amanipulated variable for bringing the estimated torque value intoagreement with the motor-mode torque command value or the generator-modetorque command value in the feedback mode. Specifically, the torquefeedback controller 129 a calculates the voltage phase command as afunction of a deviation of the estimated torque value from themotor-mode torque command value or the generator-mode torque commandvalue using PI feedback techniques.

The operation signal generator 130 a works to produce the operationsignal for the first inverter 101 using the voltage amplitude command,the voltage phase command, and the electrical angle θ. Specifically, theoperation signal generator 130 a calculates the command values for thethree-phase windings based on the voltage amplitude command, the voltagephase command, and the electrical angle θ and then generates switchingoperation signals for the upper and lower arms for the three-phasewindings by means of PWM control based on comparison of levels ofsignals derived by normalizing the three-phase command voltages usingthe power supply voltage with a level of a carrier signal, such as atriangle wave signal.

The operation signal generator 130 a may alternatively be designed toproduce the switching operation signals using pulse pattern informationthat is map information about relations among the voltage amplitudecommand, the voltage phase command, the electrical angle θ, and theswitching operation signal, the voltage amplitude command, the voltagephase command, and the electrical angle θ.

The same structure as described above is provided for the X-, Y-, andZ-phase windings. The torque calculator 128 b works to estimate a torquevalue in the X-phase, Y-phase, or the Z-phase as a function of thed-axis current and the q-axis current converted by the d-q converter122.

The torque feedback controller 129 b calculates a voltage phase commandas a manipulated variable for bringing the estimated torque value intoagreement with the motor-mode torque command value or the generator-modetorque command value in the feedback mode. Specifically, the torquefeedback controller 129 b calculates the voltage phase command as afunction of a deviation of the estimated torque value from themotor-mode torque command value or the generator-mode torque commandvalue using PI feedback techniques.

The operation signal generator 130 b works to produce the operationsignal for the second inverter 102 using the voltage amplitude command,the voltage phase command, and the electrical angle θ. Specifically, theoperation signal generator 130 b calculates the command values for thethree-phase windings based on the voltage amplitude command, the voltagephase command, and the electrical angle θ and then generates theswitching operation signals for the upper and lower arms for thethree-phase windings by means of PWM control based on comparison oflevels of signals derived by normalizing the three-phase commandvoltages using the power supply voltage with a level of a carriersignal, such as a triangle wave signal. The driver 117 then works toturn on or off the switches Sp and Sn for the three-phase windings inthe inverters 101 and 102 in response to the switching operation signalsderived by the operation signal generators 130 a and 130 b.

The operation signal generator 130 b may alternatively be designed toproduce the switching operation signals using pulse pattern informationthat is map information about relations among the voltage amplitudecommand, the voltage phase command, the electrical angle θ, and theswitching operation signal, the voltage amplitude command, the voltagephase command, and the electrical angle θ.

The rotating electrical machine 10 has a risk that generation of anaxial current may result in electrical erosion in the bearing 21 or 22.For example, when the stator winding 51 is excited or de-excited inresponse to the switching operation, a small switching time gap (i.e.,switching unbalance) may occur, thereby resulting in distortion ofmagnetic flux, which leads to the electrical erosion in the bearings 21and 22 retaining the rotating shaft 11. The distortion of magnetic fluxdepends upon the inductance of the stator 50 and creates anelectromotive force oriented in the axial direction, which results indielectric breakdown in the bearing 21 or 22 to develop the electricalerosion.

In order to avoid the electrical erosion, this embodiment is engineeredto take three measures as discussed below. The first erosion avoidingmeasure is to reduce the inductance by designing the stator 50 to have acore-less structure and also to shape the magnetic flux in the magnetunit 42 to be smooth to minimize the electrical erosion. The seconderosion avoiding measure is to retain the rotating shaft in a cantileverform to minimize the electrical erosion. The third erosion avoidingmeasure is to unify the annular stator winding 51 and the stator core 52using molding techniques using a moulding material to minimize theelectrical erosion. The first to third erosion avoiding measures will bedescribed below in detail.

In the first erosion avoiding measure, the stator 50 is designed to haveno teeth in gaps between the conductor groups 81 in the circumferentialdirection. The sealing members 57 made of non-magnetic material arearranged in the gaps between the conductor groups 81 instead of teeth(iron cores) (see FIG. 10). This results in a decrease in inductance ofthe stator 50, thereby minimizing the distortion of magnetic flux causedby the switching time gap occurring upon excitation of the statorwinding 51 to reduce the electrical erosion in the bearings 21 and 22.The inductance on the d-axis is preferably less than that on the q-axis.

Additionally, each of the magnets 91 and 92 is magnetically oriented tohave the easy axis of magnetization which is directed near the d-axis tobe more parallel to the d-axis than that near the q-axis (see FIG. 9).This strengthens the magnetic flux on the d-axis, thereby resulting in asmooth change in surface magnetic flux (i.e., an increase or decrease inmagnetic flux) from the q-axis to the d-axis on each magnetic pole ofthe magnets 91 and 92. This minimizes a sudden voltage change arisingfrom the switching imbalance to avoid the electrical erosion.

In the second erosion avoiding measure, the rotating electrical machine10 is designed to have the bearings 21 and 22 located away from theaxial center of the rotor 40 toward one of the ends of the rotor 40opposed to each other in the axial direction thereof (see FIG. 2). Thisminimizes the risk of the electrical erosion as compared with a casewhere a plurality of bearings are arranged outside axial ends of arotor. In other words, in the structure wherein the rotor has endsretained by the bearings, generation of a high-frequency magnetic fluxresults in creation of a closed circuit extending through the rotor, thestator, and the bearings (which are arranged axially outside the rotor).This leads to a risk that the axial current may result in electricalerosion in the bearings. In contrast, the rotor 40 are retained by theplurality of bearings 21 and 22 in the cantilever form, so that theabove closed circuit does not occur, thereby minimizing the electricalerosion in the bearings 21 and 22.

In addition to the above one-side layout of the bearings 21 and 22, therotating electrical machine 10 also has the following structure. In themagnet holder 41, the intermediate portion 45 extending in the radialdirection of the rotor 40 is equipped with the contact avoider whichaxially extends to avoid physical contact with the stator 50 (see FIG.2). This enables a closed circuit through which the axial current flowsthrough the magnet holder 41 to be lengthened to increase the resistancethereof. This minimizes the risk of the electrical erosion of thebearings 21 and 22.

The retainer 23 for the bearing unit 20 is secured to the housing 30 andlocated on one axial end side of the rotor 40, while the housing 30 andthe unit base 61 (i.e., a stator holder) are joined together on theother axial end of the rotor 40 (see FIG. 2). These arrangementsproperly achieve the structure in which the bearings 21 and 22 arelocated only on the one end of the length of the rotating shaft 11.Additionally, the unit base 61 is connected to the rotating shaft 11through the housing 30, so that the unit base 61 is located electricallyaway from the rotating shaft 11. An insulating member such as resin maybe disposed between the unit base 61 and the housing 30 to place theunit base 61 and the rotating shaft 11 electrically farther away fromeach other. This also minimizes the risk of the electrical erosion ofthe bearings 21 and 22.

The one-side layout of the bearings 21 and 22 in the rotating electricalmachine 10 in this embodiment decreases the axial voltage applied to thebearings 21 and 22 and also decreases the potential difference betweenthe rotor 40 and the stator 50. A decrease in the potential differenceapplied to the bearings 21 and 22 is, thus, achieved without use ofconductive grease in the bearings 21 and 22. The conductive greaseusually contains fine particles such as carbon particles, thus leadingto a risk of generation of acoustic noise. In order to alleviate theabove problem, this embodiment uses a non-conductive grease in thebearings 21 and 22 to minimize the acoustic noise in the bearings 21 and22. For instance, in a case where the rotating electrical machine 10 isused with an electrical vehicle, it is usually required to take ameasure to eliminate the acoustic noise. This embodiment is capable ofproperly taking such a measure.

In the third erosion avoiding measure, the stator winding 51 and thestator core 52 are unified together using a mouldling material tominimize a positional error of the stator winding 51 in the stator 50(see FIG. 11). The rotating electrical machine 10 in this embodiment isdesigned not to have conductor-to-conductor members (e.g., teeth)between the conductor groups 81 arranged in the circumferentialdirection of the stator winding 51, thus leading to a concern about thepositional error or misalignment of the stator winding 51. Themisalignment of the conductor of the stator winding 51 may be minimizedby unifying the stator winding 51 and the stator core 52 in the mold.This eliminates risks of the distortion of magnetic flux arising fromthe misalignment of the stator winding 51 and the electrical erosion inthe bearings 21 and 22 resulting from the distortion of the magneticflux.

The unit base 61 serving as a housing to firmly fix the stator core 52is made of carbon fiber reinforced plastic (CFRP), thereby minimizingelectrical discharge to the unit base 61 as compared with when the unitbase 61 is made of aluminum, thereby avoiding electrical erosion.

An additional erosion avoiding measure may be taken to make at least oneof the outer race 25 and the inner race 26 of each of the bearings 21and 22 using a ceramic material or alternatively to install aninsulating sleeve outside the outer race 25.

Other embodiments will be described below in terms of differencesbetween themselves and the first embodiment.

Second Embodiment

In this embodiment, the polar anisotropic structure of the magnet unit42 of the rotor 40 is changed and will be described below in detail.

The magnet unit 42 is, as clearly illustrated in FIGS. 22 and 23, madeusing a magnet array referred to as a Halbach array. Specifically, themagnet unit 42 is equipped with the first magnets 131 and the secondmagnets 132. The first magnets 131 have a magnetization direction (i.e.,an orientation of a magnetization vector thereof) oriented in the radialdirection of the magnet unit 42. The second magnets 132 have amagnetization direction (i.e., an orientation of the magnetizationvector thereof) oriented in the circumferential direction of the magnetunit 42. The first magnets 131 are arrayed at a given interval away fromeach other in the circumferential direction. Each of the second magnets132 is disposed between the first magnets 131 arranged adjacent eachother in the circumferential direction. The first magnets 131 and thesecond magnets 132 are each implemented by a rare-earth permanentmagnet, such as a neodymium magnet.

The first magnets 131 are arranged away from each other in thecircumferential direction so as to have N-poles and S-poles which arecreated in radially inner portions thereof and face the stator 50. TheN-poles and the S-poles are arranged alternately in the circumferentialdirection. The second magnets 132 are arranged to have N-poles andS-poles alternately located adjacent the first magnets 131 in thecircumferential direction. The cylinder 43 which surrounds the magnets131 and 132 may be formed as a soft magnetic core made of a softmagnetic material and which functions as a back core. The magnet unit 42in this embodiment are designed to have the easy axis of magnetizationoriented in the same way as in the first embodiment relative to thed-axis and the q-axis in the d-q axis coordinate system.

The magnetic members 133 each of which is made of a soft magneticmaterial are disposed radially outside the first magnets 131, in otherwords, close to the cylinder 43 of the magnet holder 41. Each of themagnetic members 133 may be made of magnetic steel sheet, soft iron, ora dust core material. Each of the magnetic members 133 has a lengthidentical with that of the first magnet 131 (especially, a length of anouter periphery of the first magnet 131) in the circumferentialdirection. An assembly made up of each of the first magnets 131 and acorresponding one of the magnetic members 133 has a thickness identicalwith that of the second magnet 132 in the radial direction. In otherwords, each of the first magnets 131 has the thickness smaller than thatof the second magnet 132 by that of the magnetic member 133 in theradial direction. The magnets 131 and 132 and the magnetic members 133are firmly secured to each other using, for example, adhesive agent. Inthe magnet unit 42, the radial outside of the first magnets 131 facesaway from the stator 50. The magnetic members 133 are located on theopposite side of the first magnets 131 to the stator 50 in the radialdirection (i.e., farther away from the stator 50).

Each of the magnetic members 133 has the key 134 in a convex shape whichis formed on the outer periphery thereof and protrudes radially outsidethe magnetic member 133, in other words, protrudes into the cylinder 43of the magnet holder 41. The cylinder 43 has the key grooves 135 whichare formed in an inner peripheral surface thereof in a concave shape andin which the keys 134 of the magnetic members 133 are fit. Theprotruding shape of the keys 134 is contoured to conform with therecessed shape of the key grooves 135. As many of the key grooves 135 asthe keys 134 of the magnetic members 133 are formed. The engagementbetween the keys 134 and the key grooves 135 serves to eliminatemisalignment or a positional deviation of the first magnets 131, thesecond magnets 132, and the magnet holder 41 in the circumferentialdirection (i.e. a rotational direction). The keys 134 and the keygrooves 135 (i.e., convexities and concavities) may be formed either onthe cylinders 43 of the magnet holder 41 or in the magnetic members 133,respectively. Specifically, the magnetic members 133 may have the keygrooves 135 in the outer periphery thereof, while the cylinder 43 of themagnet holder 41 may have the keys 134 formed on the inner peripherythereof.

The magnet unit 42 has the first magnets 131 and the second magnets 132alternately arranged to increase the magnetic flux density in the firstmagnets 131. This results in concentration of magnetic flux on onesurface of the magnet unit 42 to enhance the magnetic flux close to thestator 50.

The layout of the magnetic members 133 radially arranged outside thefirst magnets 131, in other words, farther away from the stator 50reduces partial magnetic saturation occurring radially outside the firstmagnets 131, thereby alleviating a risk of demagnetization in the firstmagnets 131 arising from the magnetic saturation. This results in anincrease in magnetic force produced by the magnet unit 42. In otherwords, the magnet unit 42 in this embodiment is viewed to have portionswhich are usually subjected to the demagnetization and replaced with themagnetic members 133.

FIGS. 24(a) and 24(b) are illustrations which demonstrate flows ofmagnetic flux in the magnet unit 42. FIG. 24(a) illustrates aconventional structure in which the magnet unit 42 is not equipped withthe magnetic members 133. FIG. 24(b) illustrates the structure in thisembodiment in which the magnet unit 42 is equipped with the magneticmembers 133. FIGS. 24(a) and 24(b) are linearly developed views of thecylinder 43 of the magnet holder 41 and the magnet unit 42. Lower sidesof FIGS. 24(a) and 24(b) are close to the stator 50, while upper sidesthereof are farther away from the stator 50.

In the structure shown in FIG. 24(a), a magnetic flux-acting surface ofeach of the first magnets 131 and a side surface of each of the secondmagnets 132 are placed in contact with the inner peripheral surface ofthe cylinder 43. A magnetic flux-acting surface of each of the secondmagnets 132 is placed in contact with the side surface of one of thefirst magnets 131. Such layout causes a combined magnetic flux to becreated in the cylinder 43. The combined magnetic flux is made up of amagnetic flux F1 which passes outside the second magnet 132 and thenenters the surface of the first magnets 131 contacting the cylinder 43and a magnetic flux which flows substantially parallel to the cylinder43 and attracts a magnetic flux F2 produced by the second magnet 132.This leads to a risk that the magnetic saturation may occur near thesurface of contact between the first magnet 131 and the second magnet132 in the cylinder 43

In the structure in FIG. 24(b) wherein each of the magnetic members 133is disposed between the magnetic flux-acting surface of the first magnet131 and the inner periphery of the cylinder 43 farther away from thestator 50, the magnetic flux is permitted to pass through the magneticmember 133. This minimizes the magnetic saturation in the cylinder 43and increases resistance against the demagnetization.

The structure in FIG. 24(b), unlike FIG. 24(a), functions to eliminatethe magnetic flux F2 facilitating the magnetic saturation. Thiseffectively enhances the permeance in the whole of the magnetic circuit,thereby ensuring the stability in properties of the magnetic circuitunder elevated temperature.

As compared with radial magnets used in conventional SPM rotors, thestructure in FIG. 24(b) has an increased length of the magnetic pathpassing through the magnet. This results in a rise in permeance of themagnet which enhances the magnetic force to increase the torque.Further, the magnetic flux concentrates on the center of the d-axis,thereby increasing the sine wave matching percentage. Particularly, theincrease in torque may be achieved effectively by shaping the waveformof the current to a sine or trapezoidal wave under PWM control or using120° excitation switching ICs

In a case where the stator core 52 is made of magnetic steel sheets, thethickness of the stator core 52 in the radial direction thereof ispreferably half or greater than half the thickness of the magnet unit 42in the radial direction. For instance, it is preferable that thethickness of the stator core 52 in the radial direction is greater thanhalf the thickness of the first magnets 131 arranged at the pole-to-polecenter in the magnet unit 42. It is also preferable that the thicknessof the stator core 52 in the radial direction is smaller than that ofthe magnet unit 42. In this case, a magnet magnetic flux isapproximately 1 T, while the saturation magnetic flux density in thestator core 52 is 2 T. The leakage of magnetic flux to inside the innerperiphery of the stator core 52 is avoided by selecting the thickness ofthe stator core 52 in the radial direction to be greater than half thatof the magnet unit 42.

Magnets arranged to have the Halbach structure or the polar anisotropicstructure usually have an arc-shaped magnetic path, so that the magneticflux may be increased in proportion to a thickness of ones of themagnets which handle a magnetic flux in the circumferential direction.In such a structure, the magnetic flux flowing through the stator core52 is thought of as not exceeding the magnetic flux flowing in thecircumferential direction. In other words, when the magnetic fluxproduced by the magnets is 1 T, while ferrous metal whose saturationmagnetic flux density is 2 T is used to make the stator core 52, a lightweight and compact electrical rotating machine may be produced byselecting the thickness of the stator core 52 to be greater than halfthat of the magnets. The demagnetizing field is usually exerted by thestator 50 on the magnetic field produced by the magnets, so that themagnetic flux produced by the magnets will be 0.9 T or less. Themagnetic permeability of the stator core may, therefore, be properlykept by selecting the thickness of the stator core to be half that ofthe magnets.

Modifications of the above structure will be described below.

First Modification

In the above embodiment, the outer peripheral surface of the stator core52 has a curved surface without any irregularities. The plurality ofconductor groups 81 are arranged at a given interval away from eachother on the outer peripheral surface of the stator core 52. This layoutmay be changed. For instance, the stator core 52 illustrated in FIG. 25is equipped with the circular ring-shaped yoke 141 and the protrusions142. The yoke 141 is located on the opposite side (i.e., a lower side,as viewed in the drawing) of the stator winding 51 to the rotor 40 inthe radial direction. Each of the protrusions 142 protrudes into a gapbetween a respective two of the straight sections 83 arranged adjacenteach other in the circumferential direction. The protrusions 142 arearranged at a given interval away from each other in the circumferentialdirection radially outside the yoke 141, i.e., close to the rotor 40.Each of the conductor groups 81 of the stator winding 51 engages theprotrusions 142 in the circumferential direction, in other words, theprotrusions 142 are used as positioners to position and array theconductor groups 81 in the circumferential direction. The protrusions142 correspond to conductor-to-conductor members.

A radial thickness of each of the protrusions 142 from the yoke 141, inother words, a distance W, as illustrated in FIG. 25, between the innersurface 320 of the straight sections 82 which is placed in contact withthe yoke 141 and the top of the protrusion 412 in the radial directionof the yoke 141 is selected to be smaller than half a radial thickness(as indicated by H1 in the drawing) of the straight sections 83 arrangedadjacent the yoke 141 in the radial direction. In other words,non-conductive members (i.e., the sealing members 57) preferably eachoccupy three-fourths of a dimension (i.e., thickness) T1 (i.e., twicethe thickness of the conductors 82, in other words, a minimum distancebetween the surface 320 of the conductor group 81 placed in contact withthe stator core 52 and the surface 330 of the conductor group 81 facingthe rotor 40) of the conductor groups (i.e., conductors) 81 in theradial direction of the stator winding 51 (i.e., the stator core 52).Such selection of the thickness of the protrusions 142 causes each ofthe protrusions 142 not to function as a tooth between the conductorgroups 81 (i.e., the straight sections 83) arranged adjacent each otherin the circumferential direction, so that there are no magnetic pathswhich would usually be formed by the teeth. The protrusions 142 need notnecessarily to be arranged between a respective circumferentiallyadjacent two of all the conductor groups 81, but however, a singleprotrusion 142 may be disposed at least only between two of theconductor groups 81 which are arranged adjacent each other in thecircumferential direction. For instance, the protrusions 142 may bedisposed away from each other in the circumferential direction at equalintervals each of which corresponds to a given number of the conductorgroups 81. Each of the protrusions 142 may be designed to have anyshape, such as a rectangular or arc-shape.

The straight sections 83 may alternatively be arranged in a single layeron the outer peripheral surface of the stator core 52. In a broad sense,the thickness of the protrusions 142 from the yoke 141 in the radialdirection may be smaller than half that of the straight sections 83 inthe radial direction.

If an imaginary circle whose center is located at the axial center ofthe rotating shaft 11 and which passes through the radial centers of thestraight sections 83 placed adjacent the yoke 141 in the radialdirection is defined, each of the protrusions 142 may be shaped toprotrude only within the imaginary circle, in other words, not toprotrude radially outside the imaginary circle toward the rotor 40.

The above structure in which the protrusions 142 have the limitedthickness in the radial direction and do not function as teeth in thegaps between the straight sections 83 arranged adjacent each other inthe circumferential direction enables the adjacent straight sections 83to be disposed closer to each other as compared with a case where teethare provided in the gaps between the straight sections 83. This enablesa sectional area of the conductor body 82 a to be increased, therebyreducing heat generated upon excitation of the stator winding 51. Theabsence of the teeth enables magnetic saturation to be eliminated toincrease the amount of electrical current delivered to the statorwinding 51. It is, however, possible to alleviate the adverse effectsarising from an increase in amount of heat generated by the increase inelectrical current delivered to the stator winding 51. The statorwinding 51, as described above, has the turns 84 which are shifted inthe radial direction and equipped with the interference avoidingportions with the adjacent turns 84, thereby enabling the turns 84 to bedisposed away from each other in the radial direction. This enhances theheat dissipation from the turns 84. The above structure is enabled tooptimize the heat dissipating ability of the stator 50.

The radial thickness of the protrusions 142 may not be restricted by thedimension H1 in FIG. 25 as long as the yoke 141 of the stator core 52and the magnet unit 42 (i.e., each of the magnets 91 and 92) of therotor 40 are arranged at a given distance away from each other.Specifically, the radial thickness of the protrusions 142 may be largerthan or equal to the dimension H1 in FIG. 25 as long as the yoke 141 andthe magnet unit 42 arranged 2 mm or more away from each other. Forinstance, in a case where the radial thickness of the straight section83 is larger than 2 mm, and each of the conductor groups 81 is made upof the two conductors 82 stacked in the radial direction, each of theprotrusions 142 may be shaped to occupy a region ranging to half thethickness of the straight section 83 not contacting the yoke 141, i.e.,the thickness of the conductor 82 located farther away from the yoke141. In this case, the above beneficial advantages will be obtained byincreasing the conductive sectional area of the conductor groups 81 aslong as the radial thickness of the protrusions 142 is at least H1×3/2.

The stator core 52 may be designed to have the structure illustrated inFIG. 26. FIG. 26 omits the sealing members 57, but the sealing members57 may be used. FIG. 26 illustrates the magnet unit 42 and the statorcore 52 as being arranged linearly for the sake of simplicity.

In the structure of FIG. 26, the stator 50 has the protrusions 142 asconductor-to-conductor members each of which is arranged between arespective two of the conductors 82 (i.e., the straight sections 83)located adjacent each other in the circumferential direction. The stator50 is equipped with the portions 350 each of which magnetically operatesalong with one of the magnetic poles (i.e., an N-pole or an S-pole) ofthe magnet unit 42 when the stator winding 51 is excited. The portions350 extend in the circumferential direction of the stator 50. If each ofthe portions 350 has a length Wn in the circumferential direction of thestator 50, the sum of widths of the protrusions 142 lying in a range ofthis length Wn (i.e., the total dimension of the protrusions 412 in thecircumferential direction of the stator 50 in the range of length Wn) isdefined as Wt, the saturation magnetic flux density of the protrusions412 is defined as Bs, a width of the magnet unit 42 equivalent to one ofthe magnetic poles of the magnet unit 42 in the circumferentialdirection of the magnet unit 42 is defined as Wm, and the remanent fluxdensity in the magnet unit 42 is defined as Br, the protrusions 142 aremade of a magnetic material meeting a relation of

Wt×Bs≤Wm×Br  (1)

The range Wn is defined to contain ones of the conductor groups 81 whichare arranged adjacent each other in the circumferential direction andwhich overlap in time of excitation thereof with each other. It isadvisable that a reference (i.e., a border) used in defining the rangeWn be set to the center of the gap 56 between the conductor groups 81.For instance, in the structure illustrated in FIG. 26, the plurality ofconductor groups 81 lying in the range Wn include the first, the second,the third, and the fourth conductor groups 81 where the first conductorgroup 81 is closest to the magnetic center of the N-pole. The range Wnis defined to include the total of those four conductor groups 81. Ends(i.e., outer limits) of the range Wn are defined to lie at the centersof the gaps 56.

In FIG. 26, the range Wn contains half of the protrusion 142 inside eachof the ends thereof. The total of the four protrusions 142 lie in therange Wn. If the width of each of the protrusions 142 (i.e., a dimensionof the protrusion 142 in the circumferential direction of the stator 50,in other words, an interval between the adjacent conductor groups 81) isdefined as A, the sum of widths Wt of the protrusions 142 lying in therange Wn meets a relation of Wt=½A+A+A+A+½A=4A.

Specifically, the three-phase windings of the stator winding 51 in thisembodiment are made in the form of distributed windings. In the statorwinding 51, the number of the protrusions 142 for each pole of themagnet unit 42, that is, the number of the gaps 56 each between theadjacent conductor groups 81 is selected to be “the number of phases×Q”where Q is the number of the conductors 82 for each phase which areplaced in contact with the stator core 52. In other words, in the casewhere the conductors 82 are stacked in the radial direction of the rotor40 to constitute each of the conductor groups 81, Q is the number ofinner ones of the conductors 82 of the conductor groups 81 for eachphase. In this case, when the three-phase windings of the stator winding51 are excited in a given sequence, the protrusions 142 for two of thethree-phases within each pole are magnetically excited. The totalcircumferential width Wt of the protrusions 142 excited upon excitationof the stator winding 51 within a range of each pole of the magnet unit42, therefore, meets a relation of “the number of the phasesexcited×Q×A=2×2×A where A is the width of each of the protrusions 142(i.e., the gap 56) in the circumferential direction.

The total width Wt is determined in the above way. Additionally, theprotrusions 142 of the stator core 52 are made of magnetic materialmeeting the above equation (1). The total width Wt is also viewed asbeing equivalent to a circumferential dimension of where the relativemagnetic permeability is expected to become greater than one within eachpole. The total width Wt may alternatively be determined as acircumferential width of the protrusions 142 in each pole with somemargin. Specifically, since the number of the protrusions 142 for eachpole of the magnet unit 42 is given by the number of phases×Q, the widthof the protrusions 412 in each pole (i.e., the total width Wt) may begiven by the number of phases×Q×A=3×2×A=6A.

The distributed winding, as referred to herein, means that there is apair of poles (i.e., the N-pole and the S-pole) of the stator winding 51for each pair of magnetic poles. The pair of poles of the stator winding51, as referred to herein, is made of the two straight sections 83 inwhich electrical current flows in opposite directions and the turn 84electrically connecting them together. Note that a short pitch windingor a full pitch winding may be viewed as an equivalent of thedistributed winding as long as it meets the above conditions.

Next, the case of a concentrated winding will be described below. Theconcentrated winding, as referred to herein, means that the width ofeach pair of magnetic poles is different from that of each pair of polesof the stator winding 51. An example of the concentrated windingincludes a structure in which there are three conductor groups 81 foreach pair of magnetic poles, in which there are three conductor groups81 for two pairs of magnetic poles, in which there are nine conductorgroups 81 for four pairs of magnetic poles, or in which there are nineconductor groups 81 for five pairs of magnetic poles.

In the case where the stator winding 51 is made in the form of theconcentrated winding, when the three-phase windings of the statorwinding 51 are excited in a given sequence, a portion of the statorwinding 51 for two phases is excited. This causes the protrusions 142for two phases to be magnetically excited. The circumferential width Wtof the protrusions 142 which is magnetically excited upon excitation ofthe stator winding in a range of each pole of the magnet unit 42 isgiven by Wt=A×2. The width Wt is determined in this way. The protrusions142 are made of magnetic material meeting the above equation (1). In theabove described case of the concentrated winding, the sum of widths ofthe protrusions 142 arranged in the circumferential direction of thestator 50 within a region surrounded by the conductor groups 81 for thesame phase is defined as A. The dimension Wm in the concentrated windingis given by [an entire circumference of a surface of the magnet unit 42facing the air gap]×[the number of phases]÷[the number of thedistributed conductor groups 81].

Usually, a neodymium magnet, a samarium-cobalt magnet, or a ferritemagnet whose value of BH is higher than or equal to 20[MGOe(kJ/m{circumflex over ( )}3)] has Bd=1.0 T or more. Iron has Br=2.0 T ormore. The protrusions 142 of the stator core 52 may, therefore, be madeof magnetic material meeting a relation of Wt<½×Wm for realizing ahigh-power motor.

In a case where each of the conductors 82 is, as described later,equipped with the outer coated layer 182, the conductors 82 may bearranged in the circumferential direction of the stator core with theouter coated layers 182 placed in contact with each other. In this case,the width Wt may be viewed to be zero or equivalent to thicknesses ofthe outer coated layers 182 of the conductors 82 contacting with eachother.

The structure illustrated in FIG. 25 or 26 is designed to haveconductor-to-conductor members (i.e., the protrusions 142) which are toosmall in size for the magnet-produced magnetic flux in the rotor 40. Therotor 40 is implemented by a surface permanent magnet rotor which has aflat surface and a low inductance, and does not have a salient pole interms of a magnetic resistance. Such a structure enables the inductanceof the stator 50 to be decreased, thereby reducing a risk of distortionof the magnetic flux caused by the switching time gap in the statorwinding 51, which minimizes the electrical erosion of the bearings 21and 22.

Second Modification

The stator 50 equipped with the conductor-to-conductor members made tomeet the above equation may be designed to have the following structure.In FIG. 27, the stator core 52 is equipped with the teeth 143 asconductor-to-conductor members which are formed in an outer peripheralportion (an upper portion, as viewed in the drawing) of the stator core52. The teeth 143 protrude from the yoke 141 and are arranged at a giveninterval away from each other in the circumferential direction of thestator core 52. Each of the teeth 143 has a thickness identical withthat of the conductor group 81 in the radial direction. The teeth 143have side surfaces placed in contact with the conductors 82 of theconductor groups 81. The teeth 143 may alternatively be located awayfrom the conductors 82 through gaps.

The teeth 143 are shaped to have a restricted width in thecircumferential direction. Specifically, each of the teeth 143 has astator tooth which is very thin for the volume of magnets. Such astructure of the teeth 143 serves to achieve saturation by themagnet-produced magnetic flux at 1.8 T or more to reduce the permeance,thereby decreasing the inductance.

If a surface area of a magnetic flux-acting surface of the magnet unit42 facing the stator 50 for each pole is defined as Sm, and the remanentflux density of the magnet unit 42 is defined as Br, the magnetic fluxin the magnet unit 42 will be Sm×Br. A surface area of each of the teeth143 facing the rotor 40 is defined as St. The number of the conductors83 for each phase is defined as m. When the teeth 143 for two phaseswithin a range of one pole are magnetically excited upon excitation ofthe stator winding 51, the magnetic flux in the stator 50 is expressedby St×m×2×Bs. The decrease in inductance may be achieved by selectingthe dimensions of the teeth 143 to meet a relation of

St×m×2×Bs<Sm×Br  (2).

In a case where the dimension of the magnet unit 42 is identical withthat of the teeth 143 in the axial direction, the above equation (2) maybe rewritten as an equation (3) of Wst×m×2×Bs<Wm×Br where Wm is thecircumferential width of the magnet unit 42 for each pole, and Wst isthe circumferential width of the teeth 143. For example, when Bs=2 T,Br=1 T, and m=2, the equation (3) will be Wst<Wm/8. In this case, thedecrease in inductance may be achieved by selecting the width Wst of theteeth 143 to be smaller than one-eighth (⅛) of the width Wm of themagnet unit 42 for one pole. When m is one, the width Wst of the teeth143 is preferably selected to be smaller than one-fourth (¼) of thewidth Wm of the magnet unit 42 for one pole.

“Wst×m×2” in the equation (3) corresponds to a circumferential width ofthe teeth 143 magnetically excited upon excitation of the stator winding51 in a range of one pole of the magnet unit 42.

The structure in FIG. 27 is, like in FIGS. 25 and 26, equipped with theconductor-to-conductor members (i.e., the teeth 143) which are verysmall in size for the magnet-produced magnetic flux in the rotor 40.Such a structure is capable of reducing the inductance of the stator 50to alleviate a risk of distortion of the magnetic flux arising from theswitching time gap in the stator winding 51, which minimizes theprobability of the electrical erosion of the bearings 21 and 22. Notethat the definitions of parameters, such as Wt, Wn, A, and Bs,associated with the stator 50 or parameters, such as Wm and Br,associated with the magnet unit 42 may refer to those in the abovedescribed first modification.

Third Modification

The above embodiment has the sealing members 57 which cover the statorwinding 51 and occupy a region including all of the conductor groups 81radially outside the stator core 52, in other words, lie in a regionwhere the thickness of the sealing members 57 is larger than that of theconductor groups 81 in the radial direction. This layout of the sealingmembers 57 may be changed. For instance, the sealing members 57 may be,as illustrated in FIG. 28, designed so that the conductors 82 protrudepartially outside the sealing members 57. Specifically, the sealingmembers 57 are arranged so that portions of the conductors 82 that areradially outermost portions of the conductor groups 81 are exposedoutside the sealing members 57 toward the stator 50. In this case, thethickness of the sealing members 57 in the radial direction may beidentical with or smaller than that of the conductor groups 81.

Fourth Modification

The stator 50 may be, as illustrated in FIG. 29, designed not to havethe sealing members 57 covering the conductor groups 81, i.e., thestator winding 51. In this case, a gap is created between the adjacentconductor groups 81 arranged in the circumferential direction without aconductor-to-conductor member therebetween. In other words, noconductor-to-conductor member is disposed between the conductor groups81 arranged in the circumferential direction. Air may be arranged in thegaps between the conductor groups 81. The air may be viewed as anon-magnetic member or an equivalent thereof whose Bs is zero (0).

Fifth Modification

The conductor-to-conductor members of the stator 50 may be made of anon-magnetic material other than resin. For instance, a non-metallicmaterial, such as SUS304 that is austenitic stainless steel.

Sixth Modification

The stator 50 may be designed not to have the stator core 52.Specifically, the stator 50 is made of the stator winding 51 shown inFIG. 12. The stator winding 51 of the stator 50 may be covered with asealing member. The stator 50 may alternatively be designed to have anannular winding retainer made from non-magnetic material such assynthetic resin instead of the stator core 52 made from soft magneticmaterial.

Seventh Modification

The structure in the first embodiment uses the magnets 91 and 92arranged in the circumferential direction to constitute the magnet unit42 of the rotor 40. The magnet unit 42 may be made using an annularpermanent magnet. For instance, the annular magnet 95 is, as illustratedin FIG. 30, secured to a radially inner periphery of the cylinder 43 ofthe magnet holder 41. The annular magnet 95 is equipped with a pluralityof different magnetic poles whose magnetic polarities are arrangedalternately in the circumferential direction of the annular magnet 95.The magnet 95 lies integrally both on the d-axis and the q-axis. Theannular magnet 95 has a magnetic orientation directed in the radialdirection on the d-axis of each magnetic pole and a magnetic orientationdirected in the circumferential direction on the q-axis between themagnetic poles, thereby creating arc-shaped magnetic paths.

The annular magnet 95 may be designed to have an easy axis ofmagnetization directed parallel or near parallel to the d-axis near thed-axis and also to have an easy axis of magnetization directedperpendicular or near perpendicular to the q-axis near the q-axis,thereby creating the arc-shaped magnetic paths.

Eighth Modification

This modification is different in operation of the controller 110 fromthe above embodiment or modifications. Only differences from those inthe first embodiment will be described below.

The operations of the operation signal generators 116 and 126illustrated in FIG. 20 and the operation signal generators 130 a and 130b illustrated in FIG. 21 will first be discussed below using FIG. 31.The operations executed by the operation signal generators 116, 126, 130a, and 130 b are basically identical with each other. Only the operationof the operation signal generator 116 will, therefore, be describedbelow for the sake of simplicity.

The operation signal generator 116 includes the carrier generator 116 a,the U-phase comparator 116 bU, the V-phase comparator 116 bV, and theW-phase comparator 116 bW. The carrier generator 116 a produces andoutputs the carrier signal SigC in the form of a triangle wave signal.

The U-, V-, and W-phase comparators 116 bU, 116 bV, and 116 bW receivethe carrier signal SigC outputted by the carrier generator 116 a and theU-, V-, and W-phase command voltages produced by the three-phaseconverter 115. The U-, V-, and W-phase command voltages are produced,for example, in the form of a sine wave and outputted 120° out ofelectrical phase with each other.

The U-, V-, and W-phase comparators 116 bU, 116 bV, and 116 bW comparethe U-, V-, and W-phase command voltages with the carrier signal SigC toproduce operation signals for the switches Sp and Sn of the upper andlower arms in the first inverter 101 for the U-, V-, and W-phasewindings under PWM (Pulse Width Modulation) control. Specifically, theoperation signal generator 116 works to produce operation signals forthe switches Sp and Sn of the upper and lower arms for the U-, V-, andW-phase windings under the PWM control based on comparison of levels ofsignals derived by normalizing the U-, V-, and W-phase command voltagesusing the power supply voltage with a level of the carrier signal SigC.The driver 117 is responsive to the operation signals outputted by theoperation signal generator 116 to turn on or off the switches Sp and Snin the first inverter 101 for the U-, V-, and W-phase windings.

The controller 110 alters the carrier frequency fc of the carrier signalSigC, i.e., a switching frequency for each of the switches Sp and Sn.The carrier frequency fc is altered to be higher in a low torque rangeor a high-speed range in the rotating electrical machine 10 andalternatively lower in a high torque range in the rotating electricalmachine 10. This altering is achieved in order to minimize adeterioration in ease of control of electrical current flowing througheach of the U-, V-, and W-phase windings.

In brief, the core-less structure of the stator 50 serves to reduce theinductance in the stator 50. The reduction in inductance usually resultsin a decrease in electrical time constant in the rotating electricalmachine 10. This leads to a risk that a ripple of current flowingthrough each of the phase windings may be increased, thereby resultingin the deterioration in ease of control of the current flowing throughthe phase winding, which causes control divergence. The adverse effectsof the above deterioration on the ease of control usually become higherwhen the current (e.g., an effective value of the current) flowingthrough the winding lies in a low current region than when the currentlies in a high current range. In order to alleviate such a problem, thecontroller 110 in this embodiment is designed to alter the carrierfrequency fc.

How to alter the carrier frequency fc will be described below withreference to FIG. 32. This operation of the operation signal generator116 is executed by the controller 110 cyclically at a given interval.

First, in step S10, it is determined whether electrical current flowingthrough each of the three-phase windings 51 a lies in the low currentrange. This determination is made to determine whether torque nowproduced by the rotating electrical machine 10 lies in the low torquerange. Such a determination may be achieved according to the firstmethod or the second method, as discussed below.

First Method

The estimated torque value of the rotating electrical machine 10 iscalculated using the d-axis current and the q-axis current converted bythe d-q converter 112. If the estimated torque value is determined to belower than a torque threshold value, it is concluded that the currentflowing through the winding 51 a lies in the low current range.Alternatively, if the estimated torque value is determined to be higherthan or equal to the torque threshold value, it is concluded that thecurrent lies in the high current range. The torque threshold value isselected to be half, for example, the degree of starting torque (alsocalled locked rotor torque) in the rotating electrical machine 10.

Second Method

If an angle of rotation of the rotor 40 measured by an angle sensor isdetermined to be higher than or equal to a speed threshold value, it isdetermined that the current flowing through the winding 51 a lies in thelow current range, that is, in the high speed range. The speed thresholdvalue may be selected to be a rotational speed of the rotatingelectrical machine 10 when a maximum torque produced by the rotatingelectrical machine 10 is equal to the torque threshold value.

If a NO answer is obtained in step S10, meaning that the current lies inthe high current range, then the routine proceeds to step S11 whereinthe carrier frequency fc is set to the first frequency fL.

Alternatively, if a YES answer is obtained in step S10, then the routineproceeds to step S12 wherein the carrier frequency fc is set to thesecond frequency fH that is higher than the first frequency fL.

As apparent from the above discussion, the carrier frequency fc when thecurrent flowing through each of the three-phase windings lies in the lowcurrent range is selected to be higher than that when the current liesin the high current range. The switching frequency for the switches Spand Sn is, therefore, increased in the low current range, therebyminimizing a rise in current ripple to ensure the stability incontrolling the current.

When the current flowing through each of the three-phase windings liesin the high current range, the carrier frequency fc is selected to belower than that when the current lies in the low current range. Thecurrent flowing through the winding in the high current range usuallyhas an amplitude larger than that when the current lies in the lowcurrent range, so that the rise in current ripple arising from thereduction in inductance has a low impact on the ease of control of thecurrent. It is, therefore, possible to set the carrier frequency fc inthe high current range to be lower than that in the low current range,thereby reducing a switching loss in the inverters 101 and 102.

This modification is capable of realizing the following modes.

If a YES answer is obtained in step S10 in FIG. 32 when the carrierfrequency fc is set to the first frequency fL, the carrier frequency fcmay be changed gradually from the first frequency fL to the secondfrequency fH.

Alternatively, if a NO answer is obtained in step S10 when the carrierfrequency fc is set to the second frequency fH, the carrier frequency fcmay be changed gradually from the second frequency fH to the firstfrequency fL.

The operation signals for the switches may alternatively be producedusing SVM (Space Vector Modulation) instead of the PWM. The abovealteration of the switching frequency may also be made.

Ninth Modification

In each of the embodiments, two pairs of conductors making up theconductor groups 81 for each phase are, as illustrated in FIG. 33(a),arranged parallel to each other. FIG. 33(a) is a view which illustratesan electrical connection of the first and second conductors 88 a and 88b that are the two pairs of conductors. The first and second conductors88 a and 88 b may alternatively be, as illustrated in FIG. 33(b),connected in series with each other instead of the connection in FIG.33(a).

Three or more pairs of conductors may be stacked in the form of multiplelayers. FIG. 34 illustrates four pairs of conductors: the first tofourth conductors 88 a to 88 d which are stacked. The first conductor 88a, the second conductor 88 b, the third conductor 88 c, and the fourthconductor 88 d are arranged in this order from the stator core 52 in theradial direction.

The third and fourth conductors 88 c and 88 d are, as illustrated inFIG. 33(c), connected in parallel to each other. The first conductor 88a is connected to one of joints of the third and fourth conductors 88 cand 88 d. The second conductor 88 b is connected to the other joint ofthe third and fourth conductors 88 c and 88 d. The parallel connectionof conductors usually results in a decrease in current density of thoseconductors, thereby minimizing thermal energy produced upon energizationof the conductors. Accordingly, in the structure in which a cylindricalstator winding is installed in a housing (i.e., the unit base 61) withthe coolant path 74 formed therein, the first and second conductors 88 aand 88 b which are connected in non-parallel to each other are arrangedclose to the stator core 52 placed in contact with the unit base 61,while the third and fourth conductors 88 c and 88 d which are connectedin parallel to each other are disposed farther away from the stator core52. This layout equalizes the cooling ability of the conductors 88 a to88 d stacked in the form of multiple layers.

The conductor group 81 including the first to fourth conductors 88 a to88 d may have a thickness in the radial direction which is smaller thana circumferential width of the conductor groups 81 for one phase withina region of one pole.

Tenth Modification

The rotating electrical machine 10 may alternatively be designed to havean inner rotor structure (i.e., an inward rotating structure). In thiscase, the stator 50 may be mounted, for example, on a radial outsidewithin the housing 30, while the rotor 40 may be disposed on a radialinside within the housing 30. The inverter unit 60 may be mounted one orboth axial sides of the stator 50 or the rotor 40. FIG. 35 is atransverse sectional view of the rotor 40 and the stator 50. FIG. 36 isan enlarged view which partially illustrates the rotor 40 and the stator50 in FIG. 35.

The inner rotor structure in FIGS. 35 and 36 is substantially identicalwith the outer rotor structure in FIGS. 8 and 9 except for the layout ofthe rotor 40 and the stator 50 in the radial direction. In brief, thestator 50 is equipped with the stator winding 51 having the flattenedconductor structure and the stator core 52 with no teeth. The statorwinding 51 is installed radially inside the stator core 52. The statorcore 52, like the outer rotor structure, has any of the followingstructures.

(A) The stator 50 has the conductor-to-conductor members each of whichis disposed between the conductor portions in the circumferentialdirection. As the conductor-to-conductor members, magnetic material isused which meets a relation of Wt×Bs≤Wm×Br where Wt is a width of theconductor-to-conductor members in the circumferential direction withinone magnetic pole, Bs is the saturation magnetic flux density of theconductor-to-conductor members, Wm is a width of the magnet unitequivalent to one magnetic pole in the circumferential direction, and Bris the remanent flux density in the magnet unit.(B) The stator 50 has the conductor-to-conductor members each of whichis disposed between the conductor portions in the circumferentialdirection. The conductor-to-conductor members are each made of anon-magnetic material.(C) The stator 50 has no conductor-to-conductor member disposed betweenthe conductor portions in the circumferential direction.

The same is true of the magnets 91 and 92 of the magnet unit 42.Specifically, the magnet unit 42 is made up of the magnets 91 and 92each of which is magnetically oriented to have the easy axis ofmagnetization which is directed near the d-axis to be more parallel tothe d-axis than that near the q-axis which is defined on the boundary ofthe magnetic poles. The details of the magnetization direction in eachof the magnets 91 and 92 are the same as described above. The magnetunit 42 may be the annular magnet 95 (see FIG. 30).

FIG. 37 is a longitudinal sectional view of the rotating electricalmachine 10 designed to have the inner rotor structure. FIG. 37corresponds to FIG. 2. Differences from the structure in FIG. 2 will bedescribed below in brief. In FIG. 37, the annular stator 50 is retainedinside the housing 30. The rotor 40 is disposed inside the stator 50with an air gap therebetween to be rotatable. The bearings 21 and 22are, like in FIG. 2, offset from the axial center of the rotor 40 in theaxial direction of the rotor 40, so that the rotor 40 is retained in thecantilever form. The inverter 60 is mounted inside the magnet holder 41of the rotor 40.

FIG. 38 illustrates the inner rotor structure of the rotating electricalmachine 10 which is different from that described above. The housing 30has the rotating shaft 11 retained by the bearings 21 and 22 to berotatable. The rotor 40 is secured to the rotating shaft 11. Like thestructure in FIG. 2, each of the bearings 21 and 22 is offset from theaxial center of the rotor 40 in the axial direction of the rotor 40. Therotor 40 is equipped with the magnet holder 41 and the magnet unit 42.

The rotating electrical machine 10 in FIG. 38 is different from that inFIG. 37 in that the inverter unit 60 is not located radially inside therotor 40. The magnet holder 41 is joined to the rotating shaft 11radially inside the magnet unit 42. The stator 50 is equipped with thestator winding 51 and the stator core 52 and secured to the housing 30.Note that the definitions of parameters, such as Wt, Wn, Wm, and Bs,associated with the stator 50 or parameters, such as θ11, θ12, X1, X2,Wm, and Br, associated with the magnet unit 42 may refer to those in theabove described first embodiment or the first modification.

Eleventh Modification

The inner rotor structure of a rotating electrical machine which isdifferent from that described above will be discussed below. FIG. 39 isan exploded view of the rotating electrical machine 200. FIG. 40 is asectional side view of the rotating electrical machine 200. In thefollowing discussion, a vertical direction is based on the orientationof the rotating electrical machine 200.

The rotating electrical machine 200, as illustrated in FIGS. 39 and 40,includes the stator 203 and the rotor 204. The stator 203 is equippedwith the annular stator core 201 and the multi-phase stator winding 202.The rotor 204 is disposed inside the stator core 201 to be rotatable.The stator 203 works as an armature. The rotor 204 works as a fieldmagnet. The stator core 201 is made of a stack of silicon steel plates.The stator winding 202 is installed in the stator core 201. Although notillustrated, the rotor 204 is equipped with a rotor core and a pluralityof permanent magnet arranged in the form of a magnet unit. The rotorcore has formed therein a plurality of holes which are arranged at equalintervals away from each other in the circumferential direction of therotor core. The permanent magnets which are magnetized to havemagnetization directions changed alternately in adjacent magnetic polesare disposed in the holes of the rotor core. The permanent magnets ofthe magnet unit may be designed, like in FIG. 23, to have a Halbacharray structure or a similar structure. The permanent magnets of themagnet unit may alternatively be made of anisotropic magnets, asdescribed with reference to FIG. 9 or 30, in which the magneticorientation (i.e., the magnetization direction) extends in an arc-shapebetween the d-axis which is defined on the magnetic center and theq-axis which is defined on the boundary of the magnetic poles.

The stator 203 may be made to have one of the following structures.

(A) The stator 203 has the conductor-to-conductor members each of whichis disposed between the conductor portions in the circumferentialdirection. As the conductor-to-conductor members, magnetic material isused which meets a relation of Wt×Bs≤Wm×Br where Wt is a width of theconductor-to-conductor members in the circumferential direction withinone magnetic pole, Bs is the saturation magnetic flux density of theconductor-to-conductor members, Wm is a width of the magnet unitequivalent to one magnetic pole in the circumferential direction, and Bris the remanent flux density in the magnet unit.(B) The stator 203 has the conductor-to-conductor members each of whichis disposed between the conductor portions in the circumferentialdirection. The conductor-to-conductor members are each made of anon-magnetic material.(C) The stator 203 has no conductor-to-conductor member disposed betweenthe conductor portions in the circumferential direction.

The rotor 204 has the magnet unit which is made up of a plurality ofmagnets each of which is magnetically oriented to have the easy axis ofmagnetization which is directed near the d-axis to be more parallel tothe d-axis than that near the q-axis which is defined on the boundary ofthe magnetic poles.

The annular inverter case 211 is disposed on one end side of an axis ofthe rotating electrical machine 200. The inverter case 211 has a lowersurface placed in contact with an upper surface of the stator core 201.The inverter case 211 has disposed therein a plurality of power modules212 constituting an inverter circuit, the smoothing capacitors 213working to reduce a variation in voltage or current (i.e., a ripple)resulting from switching operations of semiconductor switches, thecontrol board 214 equipped with a controller, the current sensor 215working to measure a phase current, and the resolver stator 216 servingas a rotational speed sensor for the rotor 204. The power modules 212are equipped with IGBTs serving as semiconductor switches and diodes.

The inverter case 211 has the power connector 217 which is disposed on acircumferential edge thereof for connection with a dc circuit for abattery mounted in a vehicle. The inverter case 211 also has the signalconnector 218 which is disposed on the circumferential edge thereof forachieving transmission of signals between the rotating electricalmachine 200 and a controller installed in the vehicle. The inverter case211 is covered with the top cover 219. The dc power produced by thebattery installed in the vehicle is inputted into the power connector217, converted by the switches of the power modules 212 to analternating current, and then delivered to phase windings of the statorwinding 202.

The bearing unit 221 and the annular rear case 222 are disposed on theopposite end side of the axis of the stator core to the inverter case211. The bearing unit 221 retains a rotation axis of the rotor 204 to berotatable. The rear case 222 has the bearing unit 221 disposed therein.The bearing unit 221 is equipped with, for example, two bearings andoffset from the center of the length of the rotor 204 toward one of theends of the length of the rotor 204. The bearing unit 221 mayalternatively be engineered to have a plurality of bearings disposed onboth end sides of the stator core 201 opposed to each other in the axialdirection, so that the bearings retain both the ends of the rotationshaft. The rear case 222 is fastened to a gear case or a transmission ofthe vehicle using bolts, thereby securing the rotating electricalmachine 200 to the vehicle.

The inverter case 211 has formed therein the cooling flow path 211 athrough which cooling medium flows. The cooling flow path 211 a isdefined by closing an annular recess formed in a lower surface of theinverter case 211 by an upper surface of the stator core 201. Thecooling flow path 211 a surrounds a coil end of the stator winding 202.The cooling flow path 211 a has the module cases 212 a of the powermodules 212 disposed therein. Similarly, the rear case 222 has formedtherein the cooling flow path 222 a which surrounds a coil end of thestator winding 202. The cooling flow path 222 a is defined by closing anannular recess formed in an upper surface of the rear case 222 by alower surface of the stator core 201. Note that the definitions ofparameters, such as Wt, Wn, Wm, and Bs, associated with the stator 50 orparameters, such as θ11, θ12, X1, X2, Wm, and Br, associated with themagnet unit 42 may refer to those in the above described firstembodiment or the first modification.

Twelfth Modification

The above discussion has referred to the revolving-field type ofrotating electrical machines, but a revolving armature type of rotatingelectrical machine may be embodied. FIG. 41 illustrates the revolvingarmature type of rotating electrical machine 230.

The rotating electrical machine 230 in FIG. 41 has the bearing 232retained by the housings 231 a and 231 b. The bearing 232 retains therotating shaft 233 to be rotatable. The bearing 232 is made of, forexample, an oil-impregnated bearing in which a porous metal isimpregnated with oil. The rotating shaft 233 has secured thereto therotor 234 which works as an armature. The rotor 234 includes the rotorcore 235 and the multi-phase rotor winding 236 secured to an outerperiphery of the rotor core 235. The rotor core 235 of the rotor 234 isdesigned to have the slot-less structure. The multi-phase rotor winding236 has the flattened conductor structure as described above. In otherwords, the multi-phase rotor winding 236 is shaped to have an area foreach phase which has a dimension in the circumferential direction whichis larger than that in the radial direction.

The stator 237 is disposed radially outside the rotor 234. The stator237 works as a field magnet. The stator 237 includes the stator core 238and the magnet unit 239. The stator core 238 is secured to the housing231 a. The magnet unit 239 is attached to an inner periphery of thestator core 238. The magnet unit 239 is made up of a plurality ofmagnets arranged to have magnetic poles alternately arrayed in thecircumferential direction. Like the magnet unit 42 described above, themagnet unit 239 is magnetically oriented to have the easy axis ofmagnetization which is directed near the d-axis to be more parallel tothe d-axis than that near the q-axis that is defined on a boundarybetween the magnetic poles. The magnet unit 239 is equipped withmagnetically oriented sintered neodymium magnets whose intrinsiccoercive force is 400 [kA/m] or more and whose remanent flux density is1.0 [T] or more.

The rotating electrical machine 230 in this embodiment is engineered asa two-pole three-coil brush coreless motor. The multi-phase rotorwinding 236 is made of three coils. The magnet unit 239 is designed tohave two poles. A ratio of the number of poles and the number of coilsin typical brush motors is 2:3, 4:10, or 4:21 depending upon intendeduse.

The rotating shaft 233 has the commutator 241 secured thereto. Aplurality of brushes 242 are arranged radially outside the commutator241. The commutator 241 is electrically connected to the multi-phaserotor winding 236 through the conductors 234 embedded in the rotatingshaft 233. The commutator 241, the brushes 242, and the conductors 243are used to deliver dc current to the multi-phase rotor winding 236. Thecommutator 241 is made up of a plurality of sections arrayed in acircumferential direction thereof depending upon the number of phases ofthe multi-phase rotor winding 236. The brushes 242 may be connected to adc power supply, such as a storage battery, using electrical wires orusing a terminal block.

The rotating shaft 233 has the resinous washer 244 disposed between thebearing 232 and the commutator 241. The resinous washer 244 serves as asealing member to minimize leakage of oil seeping out of the bearing232, implemented by an oil-impregnated bearing, to the commutator 241.

Thirteenth Modification

Each of the conductors 82 of the stator winding 51 of the rotatingelectrical machine 10 may be designed to have a stack of a plurality ofinsulating coatings or layers laid on each other. For instance, each ofthe conductors 82 may be made by covering a bundle of a plurality ofinsulating layer-coated conductors (i.e., wires) with an insulatinglayer, so that the insulating layer (i.e., an inner insulating layer) ofeach of the conductors 82 is covered with the insulating layer (i.e., anouter insulating layer) of the bundle. The outer insulating layer ispreferably designed to have an insulating ability greater than that ofthe inner insulating layer. Specifically, the thickness of the outerinsulating layer is selected to be larger than that of the innerinsulating layer. For instance, the outer insulating layer has athickness of 100 μm, while the inner insulating layer has a thickness of40 μm. Alternatively, the outer insulating layer may have a permittivitylower than that of the inner insulating layer. Each of the conductors 82may have any of the above structure. Each wire is preferably made of acollection of conductive members or fibers.

As apparent from the above discussion, the rotating electrical machine10 becomes useful in a high-voltage system of a vehicle by increasingthe insulation ability of the outermost layer of the conductor 82. Theabove structure enables the rotating electrical machine 10 to be drivenin low pressure conditions such as highlands.

Fourteenth Modification

Each of the conductors 82 equipped with a stack of a plurality ofinsulating layers may be designed to have at least one of a linearexpansion coefficient and the degree of adhesion strength differentbetween an outer one and an inner one of the insulating layers. Theconductors 82 in this modification are illustrated in FIG. 42.

In FIG. 42, the conductor 82 includes a plurality of (four in thedrawing) wires 181, the outer coated layer 182 (i.e, an outer insulatinglayer) with which the wires 181 are covered and which is made of, forexample, resin, and the intermediate layer 183 (i.e., an intermediateinsulating layer) which is disposed around each of the wires 181 withinthe outer coated layer 182. Each of the wires 181 includes theconductive portion 181 a made of copper material and theconductor-coating layer (i.e., an inner insulating layer) made ofelectrical insulating material. The outer coated layer 182 serves toelectrically insulate between phase-windings of the stator winding. Eachof the wires 181 is preferably made of a collection of conductivemembers or fibers.

The intermediate layer 183 has a linear expansion coefficient higherthan that of the coated layer 181 b, but lower than that of the outercoated layer 182. In other words, the linear expansion coefficient ofthe conductor 82 is increased from an inner side to an outer sidethereof. Typically, the outer coated layer 182 is designed to have alinear expansion coefficient higher than that of the coated layer 181 b.The intermediate layer 183, as described above, has a linear expansioncoefficient intermediate between those of the coated layer 181 b and theouter coated layer 182 and thus serves as a cushion to eliminate a riskthat the inner and outer layers may be simultaneously broken.

Each of the wires 181 of the conductor 82 has the conductive portion 181a and the coated layer 181 b adhered to the conductive portion 181 a.The coated layer 181 b and the intermediate layer 183 are also adheredtogether. The intermediate layer 183 and the outer coated layer 182 areadhered together. Such joints have a strength of adhesion decreasingtoward an outer side of the conductor 82. In other words, the strengthof adhesion between the conductive portion 181 a and the coated layer181 b is lower than that between the coated layer 181 b and theintermediate layer 183 and between the intermediate layer 183 and theouter coated layers 182. The strength of adhesion between the coatedlayer 181 b and the intermediate layer 183 may be higher than oridentical with that between the intermediate layer 183 and the outercoated layers 182. Usually, the strength of adhesion between, forexample, two coated layers may be measured as a function of a tensilestrength required to peel the coated layers away from each other. Thestrength of adhesion of the conductor 82 is selected in the above way tominimize the risk that the inner and outer layers may be broken togetherarising from a temperature difference between inside and outside theconductor 82 when heated or cooled.

Usually, the heat generation or temperature change in the rotatingelectrical machine results in copper losses arising from heat from theconductive portion 181 a of the wire 181 and from an iron core. Thesetwo types of loss result from the heat transmitted from the conductiveportion 181 a in the conductor 82 or from outside the conductor 82. Theintermediate layer 183 does not have a heat source. The intermediatelayer 183 has the strength of adhesion serving as a cushion for thecoated layer 181 b and the outer coated layer 182, thereby eliminatingthe risk that the coated layer 181 b and the outer coated layer 182 maybe simultaneously broken. This enables the rotating electrical machineto be used in conditions, such as in vehicles, wherein a resistance tohigh pressure is required, or the temperature greatly changes.

In addition, the wire 181 may be made of enamel wire with a layer (i.e.,the coated layer 181 b) coated with resin, such as PA, PI or PAI.Similarly, the outer coated layer 182 outside the wire 181 is preferablymade of PA, PI, and PAI and has a large thickness. This minimizes a riskof breakage of the outer coated layer 182 caused by a difference inlinear expansion coefficient. Instead of use of PA, PI, PAI to make theouter coated layer 182 having a large thickness, material, such as PPS,PEEK, fluororesin, polycarbonate, silicon, epoxy, polyethylenenaphthalate, or LCP which has a dielectric permittivity lower than thatof PI or PAI is preferably used to increase the conductor density of therotating electrical machine. The use of such resin enhances theinsulating ability of the outer coated layer 182 even when it has athickness smaller than or equal to that of the coated layer 181 b andincreases the occupancy of the conductive portion. Usually, the aboveresin has the degree of electric permittivity higher than that of aninsulating layer of enamel wire. Of course, there is an example wherethe state of formation or additive results in a decrease in electricpermittivity thereof. Usually, PPS and PEEK is higher in linearexpansion coefficient than an enamel-coated layer, but lower thananother type of resin and thus is useful only for the outer of the twolayers.

The strength of adhesion of the two types of coated layers arrangedoutside the wire 181 (i.e., the intermediate insulating layer and theouter insulating layer) to the enamel coated layer of the wire 181 ispreferably lower than that between the copper wire and the enamel coatedlayer of the wire 181, thereby minimizing a risk that the enamel coatedlayer and the above two types of coated layers are simultaneouslybroken.

In a case where the stator is equipped with a water cooling mechanism, aliquid cooling mechanism, or an air cooling mechanism, thermal stress orimpact stress is thought of as being exerted first on the outer coatedlayers 182. The thermal stress or the impact stress is decreased bypartially bonding the insulating layer of the wire 181 and the above twotypes of coated layers together even if the insulation layer is made ofresin different from those of the above two types of coated layers. Inother words, the above described insulating structure may be created byplacing a wire (i.e., an enamel wire) and an air gap and also arranginga fluororesin, polycarbonate, silicon, epoxy, polyethylene naphthalate,or LCP. In this case, adhesive which is made from epoxy, low in electricpermittivity, and also low in linear expansion coefficient is preferablyused to bond the outer coated layer and the inner coated layer together.This eliminates breakage of the coated layers caused by friction arisingfrom vibration of the conductive portion or breakage of the outer coatedlayer due to the difference in linear expansion coefficient as well asthe mechanical strength.

The outermost layer which serves to ensure the mechanical strength orsecurement of the conductor 82 having the above structure is preferablymade from resin material, such as epoxy, PPS, PEEK, or LCP which is easyto shape and similar in dielectric constant or linear expansioncoefficient to the enamel coated layer, typically in a final process fora stator winding.

Typically, the resin potting is made using urethane or silicon. Suchresin, however, has a linear expansion coefficient approximately twicethat of other types of resin, thus leading to a risk that thermal stressis generated when the resin is subjected to the resin potting, so thatit is sheared. The above resin is, therefore, unsuitable for use whererequirements for insulation are severe and 60V or more. The finalinsulation process to make the outermost layer using injection mouldingtechniques with epoxy, PPS, PEEK, or LCP satisfies the aboverequirements.

Other modifications will be listed below.

The distance DM between a surface of the magnet unit 42 which faces thearmature and the axial center of the rotor in the radial direction maybe selected to be 50 mm or more. For instance, the distance DM, asillustrated in FIG. 4, between the radial inner surface of the magnetunit 42 (i.e., the first and second magnets 91 and 92) and the center ofthe axis of the rotor 40 may be selected to be 50 mm or more.

The small-sized slot-less structure of the rotating electrical machinewhose output is several tens or hundreds watt is known which is used formodels. The inventors of this application have not seen examples wherethe slot-less structure is used with large-sized industrial rotatingelectrical machines whose output is more than 10 kW. The inventors havestudied the reason for this.

Modern major rotating electrical machines are categorized into four maintypes: a brush motor, a squirrel-cage induction motor, a permanentmagnet synchronous motor, and a reluctance motor.

Brush motors are supplied with exciting current using brushes.Large-sized brush motors, therefore, have an increased size of brushes,thereby resulting in complex maintenance thereof. With the remarkabledevelopment of semiconductor technology, brushless motors, such asinduction motors, have been used instead. In the field of small-sizedmotors, a large number of coreless motors have also come on the marketin terms of low inertia or economic efficiency.

Squirrel-cage induction motors operate on the principle that a magneticfield produced by a primary stator winding is received by a secondarystator core to deliver induced current to bracket-type conductors,thereby creating magnetic reaction field to generate torque. In terms ofsmall-size and high-efficiency of the motors, it is inadvisable that thestator and the rotor be designed not to have iron cores.

Reluctance motors are motors designed to use a change in reluctance inan iron core. It is, thus, inadvisable that the iron core be omitted inprinciple.

In recent years, permanent magnet synchronous motors have used an IPM(Interior Permanent Magnet) rotor. Especially, most large-sized motorsuse an IPM rotor unless there are special circumstances.

IPM motors has properties of producing both magnet torque and reluctancetorque. The ratio between the magnet torque and the reluctance torque istimely controlled using an inverter. For these reasons, the IMP motorsare thought of as being compact and excellent in ability to becontrolled.

According to analysis by the inventors, torque on the surface of a rotorproducing the magnet torque and the reluctance torque is expressed inFIG. 43 as a function of the distance DM between the surface of themagnet unit which faces the armature and the center of the axis of therotor, that is, the radius of a stator core of a typical inner rotorindicated on the horizontal axis.

The potential of the magnet torque, as can be seen in the followingequation (eq1), depends upon the strength of magnetic field created by apermanent magnet, while the potential of the reluctance torque, as canbe seen in the following equation (eq2), depends upon the degree ofinductance, especially, on the q-axis.

The magnet torque=k·Ψ·Iq  (eq1)

The reluctance torque=k·(Lq−Ld)·Iq·Id  (eq2)

Comparison between the strength of magnetic field produced by thepermanent magnet and the degree of inductance of a winding using thedistance DM shows that the strength of magnetic field created by thepermanent magnet, that is, the amount of magnetic flux W is proportionalto a total area of a surface of the permanent magnet which faces thestator. In case of a cylindrical stator, such a total area is acylindrical surface area of the permanent magnet. Technically speaking,the permanent magnet has an N-pole and an S-pole, and the amount ofmagnetic flux W is proportional to half the cylindrical surface area.The cylindrical surface area is proportional to the radius of thecylindrical surface and the length of the cylindrical surface. When thelength of the cylindrical surface is constant, the cylindrical surfacearea is proportional to the radius of the cylindrical surface.

The inductance Lq of the winding depends upon the shape of the ironcore, but its sensitivity is low and rather proportional to the squareof the number of turns of the stator winding, so that it is stronglydependent upon the number of the turns. The inductance L is expressed bya relation of L=μ·N{circumflex over ( )}2×S/δ where μ is permeability ofa magnetic circuit, N is the number of turns, S is a sectional area ofthe magnetic circuit, and δ is an effective length of the magneticcircuit. The number of turns of the winding depends upon the size ofspace occupied by the winding. In the case of a cylindrical motor, thenumber of turns, therefore, depends upon the size of space occupied bythe winding of the stator, in other words, areas of slots in the stator.The slot is, as demonstrated in FIG. 44, rectangular, so that the areaof the slot is proportional to the product of a and b where a is thewidth of the slot in the circumferential direction, and b is the lengthof the slot in the radial direction.

The width of the slot in the circumferential direction becomes largewith an increase in diameter of the cylinder, so that the width isproportional to the diameter of the cylinder. The length of the slot inthe radial direction is proportional to the diameter of the cylinder.The area of the slot is, therefore, proportional to the square of thediameter of the cylinder. It is apparent from the above equation (eq2)that the reluctance torque is proportional to the square of current inthe stator. The performance of the rotating electrical machine,therefore, depends upon how much current is enabled to flow in therotating electrical machine, that is, depends upon the areas of theslots in the stator. The reluctance is, therefore, proportional to thesquare of the diameter of the cylinder for a cylinder of constantlength. Based on this fact, a relation of the magnetic torque and thereluctance torque with the distance DM is shown by plots in FIG. 43.

The magnet torque is, as shown in FIG. 43, increased linearly as afunction of the distance DM, while the reluctance torque is increased inthe form of a quadratic function as a function of the distance DM. FIG.43 shows that when the distance DM is small, the magnetic torque isdominant, while the reluctance torque becomes dominant with an increasein diameter of the stator core. The inventors of this application havearrived at the conclusion that an intersection of lines expressing themagnetic torque and the reluctance torque in FIG. 43 lies near 50 mmthat is the radius of the stator core. It seems that it is difficult fora motor whose output is 10 kW and whose stator core has a radius muchlarger than 50 mm to omit the stator core because the use of thereluctance torque is now mainstream. This is one of reasons why theslot-less structure is not used in large-sized motors.

The rotating electrical machine using an iron core in the stator alwaysfaces a problem associated with magnetic saturation of the iron core.Particularly, radial gap type rotating electrical machines have alongitudinal section of the rotating shaft which is of a fan shape foreach magnetic pole, so that the further inside the rotating electricalmachine, the smaller the width of a magnetic circuit, so that innerdimensions of teeth forming slots in the core become a factor of thelimit of performance of the rotating electrical machine. Even if a highperformance permanent magnet is used, generation of magnetic saturationin the permanent magnet will lead to a difficulty in producing arequired degree of performance of the permanent magnet. It is necessaryto design the permanent magnet to have an increased inner diameter inorder to eliminate a risk of occurrence of the magnetic saturation,which results in an increase size of the rotating electrical machine.

For instance, a typical rotating electrical machine with a distributedthree-phase winding is designed so that three to six teeth serve toproduce a flow of magnetic flux for each magnetic pole, but encounters arisk that the magnetic flux may concentrate on a leading one of theteeth in the circumferential direction, thereby causing the magneticflux not to flow uniformly in the three to six teeth. For instance, theflow of magnetic flux concentrates on one or two of the teeth, so thatthe one or two of the teeth in which the magnetic saturation isoccurring will move in the circumferential direction with rotation ofthe rotor, which may lead to a factor causing the slot ripple.

For the above reasons, it is required to omit the teeth in the slot-lessstructure of the rotating electrical machine whose distance DM is 50 mmor more to eliminate the risk of generation of the magnetic saturation.The omission of the teeth, however, results in an increase in magneticresistance in magnetic circuits of the rotor and the stator, therebydecreasing torque produced by the rotating electrical machine. Thereason for such an increase in magnetic resistance is that there is, forexample, a large air gap between the rotor and the stator. The slot-lessstructure of the rotating electrical machine whose distance DM is 50 mmor more, therefore, has room for improvement for increasing the outputtorque. There are numerous beneficial advantages to use the abovetorque-increasing structure in the slot-less structure of rotatingelectrical machines whose distance DM is 50 mm or more.

Not only the outer rotor type rotating electrical machines, but also theinner rotor type rotating electrical machines are preferably designed tohave the distance DM of 50 mm or more between the surface of the magnetunit which faces the armature and the center of the axis of the rotor inthe radial direction.

The stator winding 51 of the rotating electrical machine 10 may bedesigned to have only the single straight section 83 of the conductor 82arranged in the radial direction. Alternatively, a plurality of straightsections 83, for example, three, four, five, or six straight sections 83may be stacked on each other in the radial direction.

For example, the structure illustrated in FIG. 2 has the rotating shaft11 extending outside the ends of length of the rotating electricalmachine 10, but however, may alternatively be designed to have therotating shaft 11 protruding outside only one of the ends of therotating electrical machine 10. In this case, it is advisable that aportion of the rotating shaft 11 which is retained by the bearing unit20 in the cantilever form be located on one of the ends of the rotatingelectrical machine, and that the rotating shaft 11 protrude outside suchan end of the rotating electrical machine. This structure has therotating shaft 11 not protruding inside the inverter unit 60, thusenabling a wide inner space of the inverter unit 60, i.e., the cylinder71 to be used.

The above structure of the rotating electrical machine 10 usesnon-conductive grease in the bearings 21 and 22, but however, mayalternatively be designed to have conductive grease in the bearings 21and 22. For instance, conductive grease containing metallic particles orcarbon particles may be used.

A bearing or bearings may be mounted on only one or both axial ends ofthe rotor 40 for retaining the rotating shaft 11 to be rotatable. Forexample, the structure of FIG. 1 may have a bearing or bearings mountedon only one side or opposite sides of the inverter unit 60 in the axialdirection.

The magnet holder 41 of the rotor 40 of the rotating electrical machine10 has the intermediate portion 45 equipped with the inner shoulder 49 aand the annular outer shoulder 49 b, however, the magnet holder 41 mayalternatively be designed to have the flat intermediate portion 45without the shoulders 49 a and 49 b.

The conductor body 82 a of each of the conductors 82 of the statorwinding 51 of the rotating electrical machine 10 is made of a collectionof the wires 86, however, may alternatively be formed using a squareconductor having a rectangular cross section. The conductor 82 mayalternatively be made using a circular conductor having a circular crosssection or an oval cross section.

The rotating electrical machine 10 has the inverter unit 60 arrangedradially inside the stator 50, but however, may alternatively bedesigned not to have the inverter 60 disposed inside the stator 50. Thisenables the stator 50 to have a radial inner void space in which partsother than the inverter unit 60 may be mounted.

The rotating electrical machine 10 may be designed not to have thehousing 30. In this case, the rotor 40 or the stator 50 may be retainedby a wheel or another part of a vehicle.

In-Wheel Motor for Vehicle

Embodiments in which a rotating electrical machine is incorporated intoa hub of a wheel of a vehicle, such as, an automotive vehicle in theform of an in-wheel motor will be described below. FIG. 45 is aperspective view which illustrates the tire wheel assembly 400engineered to have an in-wheel motor structure and a surroundingstructure. FIG. 46 is a longitudinal sectional view which illustratesthe tire wheel assembly 400 and the surrounding structure. FIG. 47 is aperspective exploded view of the tire wheel assembly 400. These viewsare perspective illustrations of the tire wheel assembly 400, as viewedfrom inside the vehicle. The vehicle may use the in-wheel motorstructure in different modes. For instance, in a case where the vehicleis equipped with four wheels: two front wheel and two rear wheels,either or both of the front wheels and the rear wheel may be engineeredto have the in-wheel motor structure in this embodiment. Alternatively,the in-wheel motor structure may also be used with a vehicle equippedwith a front or a rear single wheel. The wheel motor, as referred toherein, is designed as a vehicle power unit.

The tire wheel assembly 400, as illustrated in FIGS. 45 to 47, includesthe tire 401 that is a known air inflated tire, the wheel 402 fit in thetire 401, and the rotating electrical machine 500 secured inside thewheel 402. The rotating electrical machine 500 is equipped with astationary portion including a stator and a rotating portion including arotor. The rotating electrical machine 500 is firmly attached at thestationary portion to the vehicle body and also attached at the rotatingportion to the wheel 402. The tire 401 and the wheel 402 are rotatedwith rotation of the rotating portion of the rotating electrical machine500. The structure of the rotating electrical machine 500 including thestationary portion and the rotating portion will be described later indetail.

The tire wheel assembly 400 also has peripheral devices: a suspension, asteering device, and a brake device mounted thereon. The suspensionretains the tire wheel assembly 400 secured to a vehicle body, notshown. The steering device works to turn the tire wheel assembly 400.The brake device works to apply a brake to the tire wheel assembly 400.

The suspension is implemented by an independent suspension, such astrailing arm suspension, a strut-type suspension, a wishbone suspension,or a multi-link suspension. In this embodiment, the suspension includesthe lower arm 411, the suspension arm 412, and the spring 413. The lowerarm 411 extends toward the center of the vehicle body. The suspensionarm 412 and the spring 413 extend vertically. The suspension arm 412 maybe engineered as a shock absorber whose detailed structure will beomitted in the drawings. The lower arm 411 and the suspension arm 412are joined to the vehicle body and also joined to the disc-shaped baseplate 405 secured to the stationary portion of the rotating electricalmachine 500. The lower arm 411 and the suspension arm 412 are, asclearly illustrated in FIG. 46, retained coaxially with each other bythe rotating electrical machine 500 (i.e., the base plate 405) using thesupport shafts 414 and 415.

The steering device may be implemented by a rack-and-pinion, aball-and-nut steering system, a hydraulic power steering system, or anelectronic power steering system. In this embodiment, the steeringdevice is made up of the rack unit 421 and the tie rod 422. The rackunit 421 is connected to the base plate 405 of the rotating electricalmachine 500 through the tie rod 422. Rotation of a steering shaft, notshown, will cause the rack unit 421 to be driven, thereby moving the tierod 422 in a lateral direction of the vehicle. This causes the tirewheel assembly 400 to be turned around the lower arm 411 and the supportshafts 414 and 415 of the suspension arm 412, thereby changing theorientation of the tire wheel assembly 400.

The brake device may preferably be made of a disc brake or a drum brake.In this embodiment, the brake device includes the disc rotor 431 and thebrake caliper 432. The disc rotor 431 is secured to the rotating shaft501 of the rotating electrical machine 500. The brake caliper 432 issecured to the base plate 405 of the rotating electrical machine 500.The brake caliper 432 has a brake pad which is hydraulically actuatedand pressed against the disc rotor 431 to create a brake in the form ofmechanical friction, thereby stopping rotation of the tire wheelassembly 400.

The tire wheel assembly 400 also has mounted thereon the storage duct440 in which the electrical cable H1 and the cooling pipe H2 extendingfrom the rotating electrical machine 500 are disposed. The storage duct440 extends from an end of the stationary portion of the rotatingelectrical machine 500 parallel to an end surface of the rotatingelectrical machine 500 without physical interference with the suspensionarm 412 and is firmly joined to the suspension arm 412, thereby fixing alocation of the joint of the storage duct 440 to the suspension arm 412relative to the base plate 405. This minimizes mechanical stress whicharises from vibration of the vehicle and acts on the electrical cable H1and the cooling pipe H2. The electrical cable H1 is electricallyconnected to a power supply, not shown, and an ECU, not shown, which aremounted in the vehicle. The cooling pipe H2 is connected to a radiator,not shown.

The structure of the rotating electrical machine 500 will be describedbelow in detail. This embodiment will refer to an example where therotating electrical machine 500 is designed as the in-wheel motor. Therotating electrical machine 500 is excellent in operation efficiency andoutput performance as compared with a conventional electrical motor of apower unit equipped with a speed reducer for use in vehicles. Therotating electrical machine 500 may alternatively be employed as anelectrical motor in another application other than the power unit forvehicles if it may be produced at low cost. In such a case, the rotatingelectrical machine 500 ensures high performance. The operationefficiency, as referred to herein, represents an indication used in fueleconomy tests in which automobiles are operated in given driving modes.

The outline of the rotating electrical machine 500 is shown in FIGS. 48to 51. FIG. 48 is a side elevation of the rotating electrical machine500, as viewed in an axial direction of the rotating shaft 501 (i.e.,from inside the vehicle). FIG. 49 is a longitudinal sectional view ofthe rotating electrical machine 500, as taken along the line 49-49 inFIG. 48. FIG. 50 is a transverse sectional view of the rotatingelectrical machine 500, as taken along the line 50-50 in FIG. 49. FIG.51 is an exploded sectional view of the rotating electrical machine 500.In the following discussion, a direction in which the rotating shaft 501extends outside the vehicle body will be referred to as an axialdirection, and a direction perpendicular to the length of the rotatingshaft 501 will be referred to as a radial direction in FIG. 51. In FIG.48, opposite directions extending in a circular form from a point on acenter line which passes through the center of the rotating shaft 501,in other words, the center of rotation of the rotating portion of therotating electrical machine 500 and defines the cross section 49 of therotating electrical machine 500 will be referred to as a circumferentialdirection. In other words, the circumferential direction is either aclockwise direction or a counterclockwise direction from a point on thecross section 49. In FIG. 49, the right side is an outer side of thevehicle, while the left side is an inner side of the vehicle. In otherwords, when the rotating electrical machine 500 is mounted in thevehicle, the rotor 510 which will be described later in detail isdisposed closer to the outer side of the vehicle body than the rotorcover 670 is.

The rotating electrical machine 500 in this embodiment is designed as anouter-rotor surface-magnet rotating electrical machine. The rotatingelectrical machine 500 includes the rotor 510, the stator 520, theinverter unit 530, the bearing 560, and the rotor cover 670. These partsare each arranged coaxially with the rotating shaft 501 providedintegrally with the rotor 510 and assembled in a given order in theaxial direction to complete the rotating electrical machine 500.

In the rotating electrical machine 500, the rotor 510 and the stator 520are hollow cylindrical and face each other through an air gap. Rotationof the rotating shaft 501 causes the rotor 510 to rotate radiallyoutside the stator 520. The rotor 510 works as a field generator. Thestator 520 works as an armature.

The rotor 510 includes the hollow cylindrical rotor carrier 511 and theannular magnet unit 512 secured to the rotor carrier 511. The rotatingshaft 501 is firmly joined to the rotor carrier 511.

The rotor carrier 511 includes the cylindrical portion 513. The magnetunit 512 is firmly attached to an inner circumferential surface of thecylindrical portion 513. In other words, the magnet unit 512 issurrounded by the cylindrical portion 513 of the rotor carrier 511 fromradially outside it. The cylindrical portion 513 has a first end and asecond end which are opposed to each other in the axial direction. Thefirst end faces the outside of the vehicle body. The second end facesthe base plate 405. In the rotor carrier 511, the end plate 514continues to the first end of the cylindrical portion 513. In otherwords, the cylindrical portion 513 and the end plate 514 are formed orjoined integrally with each other. The cylindrical portion 513 has anopening in the second end. The rotor carrier 511 may be made by a coldrolled steel plate having a high mechanical strength. For example, therotor carrier 511 is made of SPCC (steel plate cold commercial) or SPHC(steel plate hot commercial) which has a thickness larger than SPCC. Therotor carrier 511 may alternatively be made of forging steel or carbonfiber reinforced plastic (CFRP).

The length of the rotating shaft 501 is larger than a dimension of therotor carrier 511 in the axial direction. In other words, the rotatingshaft 501 protrudes from the open end of the rotor carrier 511 inwardlyin the vehicle to have an end on which the brake device is mounted.

The end plate 514 of the rotor carrier 511 has the center hole 514 apassing through a thickness thereof. The rotating shaft 501 passesthrough the hole 514 a of the end plate 514 and is retained by the rotorcarrier 511. The rotating shaft 501 has the flange 502 extending from ajoint of the rotor carrier 511 to the rotating shaft 501 in a directiontraversing or perpendicular to the length of the rotating shaft 501. Theflange 502 has a surface joined to an outer surface of the end plate 514which faces outside the vehicle, so that the rotating shaft 501 issecured to the rotor carrier 511. In the tire wheel assembly 400, thewheel 402 is joined to the rotating shaft 501 using fasteners, such asbolts, extending from the flange 502 outwardly in the vehicle.

The magnet unit 512 is made up of a plurality of permanent magnets whicharranged adjacent each other and whose magnetic polarities are disposedalternately in a circumferential direction of the rotor 510. The magnetunit 512, thus, has a plurality of magnetic poles arranged in thecircumferential direction. The permanent magnets are secured to therotor carrier 511 using, for example, adhesive. The magnet unit 512 hasthe same structure as that of the magnet unit 42 discussed withreference to FIGS. 8 and 9 and is made of sintered neodymium magnetswhose intrinsic coercive force is 400 [kA/m] or more and whose remanentflux density is 1.0 [T] or more.

The magnet unit 512 is, like the magnet unit 42 in FIG. 9, made of polaranisotropic magnets and includes the first magnets 91 and the secondmagnets 92 which are different in magnetic polarity from each other. Asalready described with reference to FIGS. 8 and 9, each of the magnets91 and 92, as can be seen in FIG. 9, includes the first portion 250 andthe two second portions 260 arranged on opposite sides of the firstportion 250 in the circumferential direction of the magnet unit 512. Inother words, the first portion 250 is located closer to the d-axis thanthe second portions 260 are. The second portions 260 are arranged closerto the q-axis than the first portion 250 is. The direction in which theeasy axis of magnetization 300 extends in the first portion 250 isoriented more parallel to the d-axis than the direction in which theeasy axis of magnetization 310 extends in the second portions 260. Inother words, the magnet unit 512 is engineered so that an angle θ11which the easy axis of magnetization 300 in the first portion 250 makeswith the d-axis is selected to be smaller than an angle θ12 which theeasy axis of magnetization 310 in the second portion 260 makes with theq-axis. Annular magnetic paths are, therefore, created according to thedirections of easy axes of magnetization. In each of the magnets 91 and92, the easy axis of magnetization in a region close to the d-axis maybe oriented parallel to the d-axis, while the easy axis of magnetizationin a region close to the q-axis may be oriented perpendicular to theq-axis. In brief, the magnet unit 512 is magnetically oriented to havethe easy axis of magnetization in the region close to the d-axis (i.e.,the center of the magnetic pole) which is oriented more parallel to thed-axis than in the region close to the q-axis (i.e., the boundarybetween the magnetic poles).

Accordingly, the above described structure of each of the magnets 91 and92 functions to enhance the magnet magnetic flux thereof on the d-axisand reduce a change in magnetic flux near the q-axis. This enables themagnets 91 and 92 to be produced which have a smooth change in surfacemagnetic flux from the q-axis to the d-axis on each magnetic pole. Themagnet unit 512 may be designed to have the same structure as that ofthe magnet unit 42 illustrated in FIGS. 22 and 23 or illustrated in FIG.30.

The magnet unit 512 may be equipped with a rotor core (i.e., a backyoke) which is made of a plurality of magnetic steel plates stacked inthe axial direction and arranged close to the cylindrical portion 513 ofthe rotor carrier 511, i.e., near the outer circumference thereof. Inother words, the rotor core may be disposed radially inside thecylindrical portion 513 of the rotor carrier 511, and the permanentmagnets (i.e., the magnets 91 and 92) may be arranged radially insidethe rotor core.

Referring back to FIG. 47, the cylindrical portion 513 of the rotorcarrier 511 has formed therein the recesses 513 a which are arranged ata given interval away from each other in the circumferential directionof the cylindrical portion 513 and extend in the axial direction of thecylindrical portion 513. The recesses 513 a are made, for example, usinga stamp or a press. The cylindrical portion 513, as can be seen in FIG.52, has convexities or protrusions 513 b each of which is formed on aninner circumference thereof in alignment with a respective one of therecesses 513 in the radial direction of the cylindrical portion 513. Themagnet unit 512 has formed in the outer circumference thereof therecesses 512 a each of which is fit on a respective one of theprotrusions 513 b of the cylindrical portion 513. In other words, theprotrusions 513 b of the cylindrical portion 513 are disposed in therecesses 512 a, thereby holding the magnet unit 512 from moving in thecircumferential direction of the rotor carrier 511. The protrusions 513b of the rotor carrier 511, thus, serve as stoppers to stop the magnetunit 512 from being rotated. The protrusions 513 b may alternatively beformed in a known way other than the pressing techniques.

FIG. 52 demonstrates magnetic paths which are produced by the magnets ofthe magnet unit 512 and indicated by arrows. Each of the magnetic pathsextends in an arc-shape and crosses the q-axis that is located at theboundary between the magnetic poles. Each of the magnetic paths isoriented parallel or near parallel to the d-axis in the region close tothe d-axis. The magnet unit 512 has the recesses 512 b which are formedin an inner circumferential surface thereof and located on the q-axis.The magnetic paths in the magnet unit 512 have lengths different betweena region near the stator 520 (i.e., a lower side in the drawing) and aregion far from the stator 520 (i.e., an upper side in the drawing).Specifically, the length of the magnetic path close to the stator 520 isshorter than that of the magnetic path far from the stator 520. Each ofthe recesses 512 b is located on the shortest length of the magneticpath. In other words, in view of an insufficient amount of magnetic fluxaround the shorter magnetic path, the magnet unit 512 is shaped to haveremoved portions in which the magnetic flux is weak.

Generally, the effective magnetic flux density Bd of a magnet becomeshigh with an increase in length of a magnetic circuit passing throughthe magnet. The permeance coefficient Pc and the effective magnetic fluxdensity Bd of the magnet have a relationship in which when one of thembecomes high, the other also becomes high. The structure illustrated inFIG. 52 enables the volume of the magnets to be reduced with a minimizedrisk of decrease in permeance coefficient Pc that is an indication ofthe degree of the effective magnetic flux density of the magnets. On theB-H coordinate system, an intersection of a permeance straight line anda demagnetization curve is an operating point according to theconfiguration of a magnet. The magnetic flux density on the operatingpoint represents the effective magnetic flux density Bd. The rotatingelectrical machine 500 in this embodiment is engineered to have thestator 520 in which the amount of iron is decreased and highly effectivein having the magnetic circuit crossing the q-axis.

The recesses 512 b of the magnet unit 512 may be used as air pathsextending in the axial direction, thereby enhancing the cooling abilityof the rotating electrical machine 500.

Next, the structure of the stator 520 will be described below. Thestator 520 includes the stator winding 521 and the stator core 522. FIG.53 is an exploded view of the stator winding 521 and the stator core522.

The stator winding 521 is made up of a plurality of phase-windings whichare of a hollow cylindrical shape. The stator core 522 serving as a basemember is arranged radially inside the stator winding 521. In thisembodiment, the stator winding 521 includes three-phase windings: aU-phase winding, a V-phase winding, and a W-phase winding. Each of theU-phase winding, the V-phase winding, and the W-phase winding is made oftwo layers of the conductor 523: an outer layer and an inner layerlocated radially inside the outer layer. The stator 520 is, like theabove described stator 50, designed to have a slot-less structure andthe flattened stator winding 521. The stator 520, therefore, hassubstantially the same structure of the stator 50 illustrated in FIGS. 8to 16.

The structure of the stator core 522 will be described below. The statorcore 522 is, like the above described stator core 52, made of aplurality of magnetic steel plates stacked in the axial direction in theshape of a hollow cylinder having a given thickness in the radialdirection. The stator winding 521 is mounted on a radially outercircumference of the stator core 522 which faces the rotor 510. Thestator core 522 does not have any irregularities on the outercircumferential surface thereof. In the assembly of the stator core 522and the stator winding 521, the conductors 523 of the stator winding 521are arranged adjacent each other in the circumferential direction on theouter circumferential surface of the stator core 522. The stator core522 functions as a back core.

The stator 520 may be made to have one of the following structures.

(A) The stator 520 has a conductor-to-conductor members each of which isdisposed between the conductors 523 in the circumferential direction. Asthe conductor-to-conductor members, magnetic material is used whichmeets a relation of Wt×Bs≤Wm×Br where Wt is a width of theconductor-to-conductor members in the circumferential direction withinone magnetic pole, Bs is the saturation magnetic flux density of theconductor-to-conductor members, Wm is a width of the magnet unit 512equivalent to one magnetic pole in the circumferential direction, and Bris the remanent flux density in the magnet unit 512.(B) The stator 520 has the conductor-to-conductor members each of whichis disposed between the conductors 523 in the circumferential direction.The conductor-to-conductor members are each made of a non-magneticmaterial.(C) The stator 520 has no conductor-to-conductor member disposed betweenthe conductors 523 in the circumferential direction.

The above structure of the stator 520 results in a decrease ininductance as compared with typical rotating electrical machinesequipped with teeth (i.e., iron core) which create a magnetic pathbetween conductors of a stator winding. Specifically, the structure ofthe stator 520 enables the inductance to be one-tenth or less of that inthe prior art structure. Usually, the reduction in inductance willresult in a reduction in impedance. The rotating electrical machine 500is, therefore, designed to increase output power relative to input powerto increase the degree of output torque. The rotating electrical machine500 is also enabled to produce a higher degree of output than rotatingelectrical machines which use a magnet-embedded rotor and output torqueusing impedance voltage (i.e., reluctance torque).

In this embodiment, the stator winding 521 is formed along with thestator core 522 in the form of a single unit using a resinous moldingmaterial (i.e., insulating material). The molding material occupies aninterval between a respective adjacent two of the conductors 523arranged in the circumferential direction. This structure of the stator520 is equivalent to that described in the above item (B). Theconductors 523 arranged adjacent each other in the circumferentialdirection may have surfaces which face each other in the circumferentialdirection and are placed in direct contact with each other or opposed toeach other through a small air gap therebetween. This structure isequivalent to the above item (C). When the structure in the above item(A) is used, the outer circumferential surface of the stator core 522 ispreferably shaped to have protrusions in accordance with orientation ofthe conductors 523 in the axial direction, that is, a skew angle in acase where the stator winding 521 is of a skew structure.

The structure of the stator winding 521 will be described below withreference to FIGS. 54(a) and 54(b). FIG. 54(a) is a partially developedview which illustrates an assembly of the conductors 523 arranged in theform of an outer one of two layers overlapping each other in the radialdirection of the stator winding 521. FIG. 54(b) is a partially developedwhich illustrates an assembly of the conductors 523 arranged in the formof an inner one of the two layers.

The stator winding 521 is designed as an annular distributed winding.The stator winding 521 is made up of the conductors 523 arranged in theform of two layers: an outer layer and an inner layer overlapping eachother in the radial direction of the stator winding 521. The conductors523 of the outer layer are, as can be seen in FIGS. 54(a) and 54(b),skewed at an orientation different from that of the conductors 523 ofthe inner layer. The conductors 523 are electrically insulated from eachother. Each of the conductors 523 is, as illustrated in FIG. 13,preferably made of an aggregation of wires 86. For instance, two each ofthe conductors 523 through which current flows in the same direction forthe same phase are arranged adjacent each other in the circumferentialdirection of the stator winding 521. Accordingly, in the stator winding521, a respective circumferentially arranged two of the conductors 523in each of the outer and inner layers, that is, a total four of theconductors 523 constitutes one conductor portion of the stator winding521 for each phase. The conductor portions are provided one in eachmagnetic pole.

The conductor portion is preferably shaped to have a thickness (i.e., adimension in the radial direction) which is less than a width thereof(i.e., a dimension in the circumferential direction) for each phase ineach pole. In other words, the stator winding 521 is preferably designedto have a flattened conductor structure. For instance, a total eight ofthe conductors 523: four arrayed adjacent each other in thecircumferential direction in each of the outer and inner layerspreferably define each conductor portion for each phase in the statorwinding 521. Alternatively, each of the conductors 523 may be shaped tohave a transverse section, as illustrated in FIG. 50, whose width (i.e.,a dimension in the circumferential direction) is larger than a thicknessthereof (i.e., a dimension in the radial direction). The stator winding521 may alternatively be designed to have the same structure as that ofthe stator winding 51 shown in FIG. 12. This structure, however,requires the rotor carrier 511 to have an inner chamber in which coilends of the stator winding 521 are disposed.

The stator winding 521, as can be seen in FIG. 54(a), has the coil side525 which overlaps the stator core 522 in the radial direction thereof.The coil side 525 is made up of portions of the conductors 523 whichobliquely extend or slant at a given angle to the axis of the statorwinding 521 and are arranged adjacent each other in the circumferentialdirection. The stator winding 521 also has the coil ends 526 locatedoutside the coil side 525 in the axial direction thereof. Each of thecoil ends 526 is made up of portions of the conductors 523 which areturned inwardly in the axial direction to make joints of the conductors523 of the coil side 525. FIG. 54(a) illustrates the coil side 525 andthe coil ends 526 in the outer layer of the conductors 523 of the statorwinding 521. The conductors 523 of the inner layer and the conductors523 of the outer layer are electrically connected together by the coilends 526. In other words, each of the conductors 523 of the outer layeris turned in the axial direction and leads to a respective one of theconductors 523 of the inner layer through the coil end 526. In brief, adirection in which current flows in the stator winding 521 is reversedbetween the outer and inner layers of the conductors 523 connected toextend in the circumferential direction.

The stator winding 521 has end regions defining ends thereof opposed toeach other in the axial direction and an intermediate region between theend regions. Each of the conductors 523 has skew angles differentbetween each of the end regions and the intermediate region.Specifically, the skew angle is an angle which each of the conductors523 makes with a line extending parallel to the axis of the statorwinding 521. The conductors 523, as illustrated in FIG. 55, have theskew angle θ_(s1) in the intermediate region and the skew angle θ_(s2)in the end regions which is different from the skew angle θ_(s1). Theskew angle θ_(s1) is smaller than the skew angle θ_(s2). The end regionsof the stator winding 521 are defined to partially occupy the coil side525. The skew angle θ_(s1) and the skew angle θ_(s2) are angles at whichthe conductors 523 are inclined in the axial direction of the statorwinding 521. The skew angle θ_(s1) in the intermediate region ispreferably selected to be an angle suitable for removing harmoniccomponents of magnetic flux resulting from excitation of the statorwinding 521.

The skew angle of each of the conductors 523 of the stator winding 521is, as described above, selected to be different between theintermediate region and the end regions. The skew angle θ_(s1) in theintermediate region is set smaller than the skew angle θ_(s2) in the endregions, thereby decreasing the size of the coil ends 526, but enablinga winding factor of the stator winding 521 to be increased. In otherwords, it is possible for the stator winding 521 to decrease the lengthof the coil ends 526, i.e., portions of the conductors 523 extendingoutside the stator core 522 in the axial direction without sacrificing adesired winding factor, which enables the rotating electrical machine500 to be reduced in size and the degree of torque to be increased.

An adequate range of the skew angle θ_(s1) in the intermediate regionwill be discussed below. In the case where the X conductors 523 where Xis the number of the conductors 523 are arranged in one magnetic pole ofthe stator winding 521, excitation of the stator winding 521 is thoughtof as producing an X^(th) harmonic. If the number of phases is definedas S, and the number of the conductors 523 for each phase is defined asm, then X=2×S×m. The inventor of this application has focused the factthat an X^(th) harmonic is equivalent to a combination of an (X⁻¹)^(th)harmonic and (X⁺¹)^(th) harmonic, and the X^(th) harmonic may be reducedby reducing at least either of the (X⁻¹)^(th) harmonic or the (X⁺¹)^(th)harmonic and found that the X^(th) harmonic will be reduced by selectingthe skew angle θ_(s1) to fall in a range of 360°/(X+1) to 360°/(X−1) interms of electrical angle.

For instance, if S=3, and m=2, the skew angle θ_(s1) is determined tofall in a range of 360°/13 to 360°/11 in order to decrease the 12^(th)harmonic (i.e., X=12). Specifically, the skew angle θ_(s1) is selectedfrom a range of 27.7° to 32.7°.

The skew angle θ_(s1) of each of the conductors 523 in the intermediateregion determined in the above way will facilitate or enhanceinterlinkage of magnetic fluxes, as produced by N-poles and S-poles ofthe magnets arranged alternately, in the intermediate regions of theconductors 523, thereby increasing the winding factor of the statorwinding 521.

The skew angle θ_(s2) in the end regions is determined to be larger thanthe skew angle θ_(s1) in the intermediate region of the conductors 523.The skew angle θ_(s2) is selected to meet a relation ofθ_(s1)<θ_(s2)<90°.

In the stator winding 521, the end of each of the conductors 523 of theinner layer is joined to the end of a respective one of the conductors523 of the outer layer by welding or bonding techniques. Alternatively,each of the conductors 523 of the inner layer and a respective one ofthe conductors 523 of the outer layer may be made by a single conductorwith a curved or bent portion defining an end joint thereof. In thestator winding 521, one of the ends of each phase winding, i.e., one ofthe axially opposed coil ends 526 of each phase winding is electricallyconnected to a power converter (i.e., an inverter) using, for example, abus. The structure of the stator winding 521 in which the conductors 523are joined together in ways different between the coil end 526 closer tothe bus bar and the coil end 526 farther away from the bus bar will bedescribed below.

First Structure

The conductors 523 are welded together at the coil ends 526 closer tothe bus bars, while they are connected in a way other than welding atthe coil ends 526 farther away from the bus bars. For instance, a singleconductor may be shaped to have a curved or bent portion which definesthe coil end 523 farther away from the bus bar and to make a respectivetwo of the conductors 523. The end of each phase winding is, asdescribed above, welded to the bus bar at the coil end 526 closer to thebus bar. The coil ends 526 closer to the bus bars may, therefore, bewelded together to connect the conductors 523 in a single step. Thisimproves the efficiency in producing the stator winding 521.

Second Structure

The conductors 523 are connected in a way other than welding at the coilends 526 closer to the bus bars and welded together at the coil ends 526farther away from the bus bars. In a case where the conductors 523 arewelded together at the coil ends 526 closer to the bus bars, it isnecessary to increase an interval between the bus bars and the coil ends526 in order to avoid a mechanical interference between the welds andthe bus bars. The second structure, however, eliminates such a need andenables an interval between the bus bars and the coil ends 526 to bedecreased, thereby loosing requirements for an axial dimension of thestator winding 521 or for the bus bars.

Third Structure

The conductors 523 are jointed together at all the coil ends 526 usingwelding techniques. This structure enables each of the conductors 523 tobe made of a shorter length of conductor than the above structures andalso eliminates the need for bending or curving conductors to improvethe efficiency in completing the stator winding 521.

Fourth Structure

The stator winding 521 is completed without welding the coil ends 526 ofall the conductors 523. This minimizes or eliminates welded portions ofthe stator winding 521, thereby minimizing a risk that electricalinsulation of the conductors 532 may be damaged at welds.

The stator winding 521 may be produced by preparing a weaved assembly ofconductor strips placed horizontally and then bending them into acylinder. In this case, the coil ends 526 of the conductor strips may bewelded together before the conductor strips are bent. The bending of theconductor strips into a cylinder may be achieved by wrapping theassembly of the conductor strips about a circular cylinder which isidentical in diameter with the stator core 522 or alternatively bywrapping the assembly of the conductor trips directly around the statorcore 522.

The stator winding 521 may alternatively be designed to have one of thefollowing structures.

The stator winding 521 illustrated in FIGS. 54(a) and 54(b) mayalternatively have the intermediate region and the end regions which areidentical in skew angle with each other.

The stator winding 521 illustrated in FIGS. 54(a) and 54(b) mayalternatively have the conductors 523 which are arranged adjacent eachother in the circumferential direction in the same phase and have endsjoined together using connecting conductors extending perpendicular tothe axial direction of the stator winding 521.

The stator winding 521 may be made in the form of 2×n annular layers.For example, the stator winding 521 may be shaped to have 4 or 6overlapping annular layers.

The structure of the inverter unit 530 working as a power converter unitwill be described below with reference to FIGS. 56 and 57 which areexploded sectional views. FIG. 57 illustrates two sub-assemblies ofparts of the inverter unit 530 shown in FIG. 56.

The inverter unit 530 includes the inverter housing 531, a plurality ofelectrical modules 532 disposed in the inverter housing 531 and the busbar module 533 which electrically connects the electrical modules 532together.

The inverter housing 531 includes the hollow cylindrical outer wall 541,the hollow cylindrical inner wall 542, and the bossed member 543. Theinner wall 542 is smaller in outer diameter than the outer wall 541 andarranged radially inside the outer wall 541. The bossed member 543 issecured to one of axially opposed ends of the inner wall 542. Thesemembers 541, 542, and 543 are each preferably made of an electricallyconductive material, such as carbon fiber reinforced plastic (CFRP). Theinverter housing 531 has the outer wall 541 and the inner wall 542overlapping each other in the radial direction thereof. The bossedmember 543 is, as illustrated in FIG. 57, attached to the axial end ofthe inner wall 542. FIG. 57

The stator core 522 is secured to an outer periphery of the outer wall541 of the inverter housing 531, thereby assembling the stator 520 andthe inverter unit 530 as a single unit.

The outer wall 541, as illustrated in FIG. 56, has a plurality ofgrooves or recesses 541 a, 541 b, and 541 c formed in an innerperipheral surface thereof. The inner wall 542 has a plurality ofgrooves or recesses 542 a, 542 b, and 542 c formed in an outerperipheral surface thereof. When the outer wall 541 and the inner wall542 are assembled together, three inner chambers: the annular chambers544 a, 544 b, and 544 c are, as can be seen in FIG. 57, defined by therecesses 541 a, 541 b, and 541 c and the recesses 542 a, 542 b, and 542c. The annular chamber 544 b located intermediate between the annularchambers 544 a and 544 c is used as the coolant path 545 through whichcooling water or coolant flows. The annular chambers 544 a and 544 clocated axially outside the annular chamber 544 b (i.e., the coolantpath 545) have the sealing members 546 disposed therein. The sealingmembers 546 hermetically seal the annular chamber 544 b (i.e., thecoolant path 545). The coolant path 545 will also be discussed later indetail.

The bossed member 543 includes the annular disc-shaped end plate 547 andthe boss 548 protruding from the end plate 547 into the housing 531. Theboss 548 is of a hollow cylindrical shape. Specifically, the inner wall542 has a first end and a second end which is opposed to the first endin the axial direction and closer to a protruding end of the rotatingshaft 501 (i.e., the inside of the vehicle). The bossed member 543 is,as can be seen in FIG. 51, secured to the second end of the inner wall542. In the tire wheel assembly 400 illustrated in FIGS. 45 to 47, thebase plate 405 is secured to the inverter housing 531 (morespecifically, the end plate 547 of the bossed member 543).

The inverter housing 531 is of a double-walled structure made up ofouter and inner peripheral walls overlapping each other in the radialdirection of the inverter housing 531. The outer peripheral wall of theinverter housing 531 is defined by a combination of the outer wall 541and the inner wall 542. The inner peripheral wall of the inverterhousing 531 is defined by the boss 548. In the following discussion, theouter peripheral wall defined by the outer wall 541 and the inner wall542 will also be referred to as an outer peripheral wall WA1. The innerperipheral wall defined by the boss 548 will also be referred to as aninner peripheral wall WA2.

The inverter housing 531 has an annular inner chamber which is definedbetween the outer peripheral wall WA1 and the inner peripheral wall WA2and in which the electrical modules 532 are arranged adjacent each otherin the circumferential direction thereof. The electrical modules 532 arefirmly attached to an inner periphery of the inner wall 542 usingadhesive or vises (i.e., screws). The inverter housing 531 will also bereferred to as a housing member. The electrical modules 532 will also bereferred to as electrical parts or electrical devices.

The bearing 560 is disposed inside the inner peripheral wall WA2 (i.e.,the boss 548). The bearing 560 retains the rotating shaft 501 to berotatable. The bearing 560 is designed as a hub bearing which isdisposed in the center of the wheel 402 to support the tire wheelassembly 400 to be rotatable. The bearing 560 is located to overlap therotor 510, the stator 520, and the inverter unit 530 in the radialdirection thereof. In the rotating electrical machine 500 of thisembodiment, the above described magnetic orientation of the rotor 510enables the magnet unit 512 to have a decreased thickness. The stator520, as described above, has a slot-less structure and uses flattenedconductors. This enables the magnetic circuit to have a thicknessdecreased in the radial direction, thereby increasing the volume ofspace radially inside the magnetic circuit. These arrangements enablethe magnetic circuit, the inverter unit 530, and the bearing 560 to bestacked in the radial direction. The boss 548 also serves as a bearingretainer in which the bearing 560 is disposed.

The bearing 560 is implemented by, for example, a radial ball bearing,as can be seen in FIG. 51, including the cylindrical inner race 561, thecylindrical outer race 561 which is larger in diameter than the innerrace 561 and arranged radially outside the inner race 561, and the balls563 disposed between the inner race 561 and the outer race 562. Theouter race 562 is fit in the bossed member 543, thereby securing thebearing 560 to the inverter housing 531. The inner race 561 is fit onthe rotating shaft 501. The inner race 561, the outer race 562, and theballs 563 are made of metallic material, such as carbon steel.

The inner race 561 of the bearing 560 includes the cylinder 561 a inwhich the rotating shaft 501 is disposed and the flange 561 b whichextends from an end of the cylinder 561 a in a direction perpendicularto the axis of the bearing 560. The flange 561 b is placed in contactwith an inner surface of the end plate 514 of the rotor carrier 511.After the bearing 560 is mounted on the rotating shaft 501, the rotorcarrier 511 is retained or held between the flange 502 of the rotatingshaft 501 and the flange 561 b of the inner race 561. The angle (i.e.,90° in this embodiment) which the flange 503 of the rotating shaft 501makes with the axis of the rotating shaft 501 is identical with thatwhich the flange 561 b of the inner race 561 makes with the axis of therotating shaft 501. The rotor carrier 511 is firmly held between theflanges 502 and 561 b.

The rotor carrier 511 is supported by the inner race 561 of the bearing560 from inside, thereby ensuring the stability in holding the rotorcarrier 511 relative to the rotating shaft 501 at a required angle,which achieves a desired degree of parallelism of the magnet unit 512 tothe rotating shaft 501. This enhances the resistance of the rotorcarrier 511 to mechanical vibration even though the rotor carrier 511 isdesigned to have a size increased in the radial direction.

Next, the electrical modules 532 installed in the inverter housing 531will be discussed below.

The electrical modules 532 is made up of a plurality of modules each ofwhich includes electrical devices, such as semiconductor switches, andsmoothing capacitors which constitute a power converter. Specifically,the electrical modules 532 include the switch modules 532A equipped withsemiconductor switches (i.e., power devices) and the capacitor modules532B equipped with smoothing capacitors.

A plurality of spaces 549 are, as illustrated in FIGS. 49 and 50,secured to the inner peripheral surface of the inner wall 542. Thespaces 549 each have a flat surface to which one of the electricalmodules 532 is attached. The inner peripheral surface of the inner wall542 is curved, while each of the electrical modules 532 has a flatsurface to be attached to the inner wall 542. Each of the spaces 549 is,therefore, shaped to have the flat surface which faces away from theinner wall 542. The electrical modules 532 are secured to the flatsurfaces of the spacers 549.

The spacers 549 need not necessarily to be interposed between the innerwall 542 and the electrical modules 532. For example, the inner wall 542may be shaped to have flat sections. Alternatively, each of theelectrical modules 532 may be shaped to have a curved surface attacheddirectly to the inner wall 542. The electrical modules 532 mayalternatively be secured to the inverter housing 531 in non-contact withthe inner peripheral surface of the inner wall 542. For instance, theelectrical modules 532 may be fixed on the end plate 547 of the bossedmember 543. The switch modules 532A may be secured to the innerperipheral surface of the inner wall 542 in non-contact therewith.Similarly, the capacitor modules 532B may be secured to the innerperipheral surface of the inner wall 542 in non-contact therewith.

In a case where the spacers 549 are disposed on the inner peripheralsurface of the inner wall 542, a combination of the outer peripheralwall WA1 and the spacers 549 will be referred to as a cylindricalportion. Alternatively, in a case where the spacers 549 are not used,the outer peripheral wall WA1 itself will be referred to as acylindrical portion.

The outer peripheral wall WA1 of the inverter housing 531, as describedalready, has formed therein the coolant path 545 in which cooling waterflows to cool the electrical modules 532. Instead of the cooling water,cooling oil may be used. The coolant path 545 is of an annular shapecontoured to conform with the configuration of the outer peripheral wallWA1. The cooling water passes the electrical modules 532 from anupstream to a downstream side in the coolant path 545. In thisembodiment, the coolant path 545 extends in an annular shape andsurrounds or overlaps the electrical modules 532 in the radialdirection.

The inner wall 542 has formed therein the inlet path 571 through whichthe cooling water is inputted into the coolant path 545 and the outletpath 572 through which the cooling water is discharged from the coolantpath 545. The inner wall 542, as described already, has the electricalmodules 532 disposed on the inner peripheral surface thereof. Only oneof intervals each between a respective circumferentially adjacent two ofthe electrical modules 532 is shaped to be larger than the others. Insuch a large interval, a portion of the inner wall 542 protrudesradially inwardly to form the bulging portion 573. The bulging portion573 has formed therein the inlet path 571 and the outlet path 572 whichare arranged adjacent each other in the circumferential direction of theinner wall 542.

FIG. 58 illustrates the layout of the electrical modules 532 in theinverter housing 531. FIG. 58 represents the same longitudinal sectionof the rotating electrical machine 500 as in FIG. 50.

The electrical modules 532 are, as can be seen in FIG. 58, arranged atthe first interval INT1 or the second interval INT2 away from each otherin the circumferential direction of the rotating electrical machine 500.Only selected two of the electrical modules 532 are, as clearlyillustrated in FIG. 58, located at the second interval INT2 away fromeach other. The second interval INT2 is selected to be larger than thefirst interval INT1. Each of the intervals INT1 and INT2 is, forexample, a distance between the centers of an adjacent two of theelectrical modules 532 arranged in the circumferential direction. Thebulging portion 573 is located in the interval INT2 between theelectrical modules 532. In other words, the intervals between theelectrical modules 532 include a longer interval (i.e., the secondinterval INT2) in which the bulging portion 573 lies.

Each of the intervals INT1 and INT2 may be given by an arc-shapeddistance between the two adjacent electrical modules 532 along a circlearound the center defined on the rotating shaft 501. Each of theintervals INT1 and INT2 may alternatively be expressed, as illustratedin FIG. 58, by an angular interval θi1 or θi2 around the center definedon the rotating shaft 501 where θi1<θi2).

In the structure illustrated in FIG. 58, the electrical modules 532 areplaced in non-contact with each other in the circumferential directionof the rotating electrical machine 500, but however, they may bearranged in contact with each other in the circumferential directionexcept for the second interval INT2.

Referring back to FIG. 48, the end plate 547 of the bossed member 543has formed therein the inlet/outlet port 574 in which ends of the inletpath 571 and the outlet path 572 are formed. The inlet path 571 and theoutlet path 572 connect with the circulation path 575 through which thecooling water is circulated. The circulation path 575 is defined by acoolant pipe. The circulation path 575 has the pump 576 and the heatdissipating device 577 installed therein. The pump 576 is actuated tocirculate the cooling water in the coolant path 545 and the circulationpath 575. The pump 576 is implemented by an electrically powered pump.The heat dissipating device 577 is made of a radiator working to releasethermal energy of the cooling water to air.

The stator 520 is, as illustrated in FIG. 50, arranged outside the outerperipheral wall WA1. The electrical modules 532 are arranged inside theouter peripheral wall WA1. Accordingly, thermal energy generated by thestator 520 is transferred to the outer peripheral wall WA1 from outside,while thermal energy generated by the electrical modules 532 istransferred to the outer peripheral wall WA1 from inside. The coolingwater flowing through the coolant path 545, therefore, simultaneouslyabsorbs the thermal energy generated by both the stator 520 and theelectrical modules 532, thereby facilitating dissipation of heat fromthe rotating electrical machine 500.

The electrical structure of the power converter will be described belowwith reference to FIG. 59.

The stator winding 521 is, as illustrated in FIG. 59, made up of aU-phase winding, a V-phase winding, and a W-phase winding. The statorwinding 521 connects with the inverter 600. The inverter 600 is made ofa bridge circuit having as many upper and lower arms as the phases ofthe stator winding 521. The inverter 600 is equipped with aseries-connected part made up of the upper arm switch 601 and the lowerarm switch 602 for each phase. Each of the switches 601 and 602 isturned on or off by a corresponding of the driver circuits 603 toenergize or deenergize a corresponding one of the phase windings. Eachof the switches 601 and 602 is made of, for example, a semiconductorswitch, such as a MOSFET or IGBT. The capacitor 604 is also connected toeach of the series-connected parts made up of the switches 601 and 602to output electrical charge required to achieve switching operations ofthe switches 601 and 602.

The control device 607 serves as a controller and is made up of amicrocomputer equipped with a CPU and memories. The control device 607analyzes information about parameters sensed in the rotating electricalmachine 500 or a request for a motor mode or a generator mode in whichthe rotating electrical machine 500 operates to control switchingoperations of the switches 601 and 602 to excite or deexcite the statorwinding 521. For instance, the control device 607 performs a PWMoperation at a given switching frequency (i.e., carrier frequency) or anoperation using a rectangular wave to turn on or off the switches 601and 602. The control device 607 may be designed as a built-in controllerinstalled inside the rotating electrical machine 500 or an externalcontroller located outside the rotating electrical machine 500.

The rotating electrical machine 500 in this embodiment has a decreasedelectrical time constant because the stator 520 is engineered to have adecreased inductance. It is, therefore, preferable to increase theswitching frequency (i.e., carrier frequency) and enhance the switchingspeed in the rotating electrical machine 500. In terms of suchrequirements, the capacitor 604 serving as a charge supply capacitor isconnected parallel to the series-connected part made up of the switches601 and 602 for each phase of the stator winding 521, thereby reducingthe wiring inductance, which deals with electrical surges even throughthe switching speed is enhanced.

The inverter 600 is connected at a high potential terminal thereof to apositive terminal of the dc power supply 605 and at a low potentialterminal thereof to a negative terminal (i.e., ground) of the dc powersupply 605. The smoothing capacitor 606 is connected to the high and lowpotential terminals of the inverter 600 in parallel to the dc powersupply 605.

Each of the switch modules 532A includes the switches 601 and 602 (i.e.,semiconductor switching devices generating heat), the driver circuits603 (i.e., electric devices constituting the driver circuits 603), andthe charge supply capacitor 604. Each of the capacitor modules 532Bincludes the smoothing capacitor 606 generating heat. The structure ofthe switch modules 532A is shown in FIG. 60.

Each of the switch modules 532A, as illustrated in FIG. 60, includes themodule case 611, the switches 601 and 602 for one of the phases of thestator winding 521, the driver circuits 603, and the charge supplycapacitor the charge supply capacitor 604. Each of the driver circuits603 is made of a dedicated IC or a circuit board and installed in theswitch module 532A.

The module case 611 is made from insulating material, such as resin. Themodule case 611 is secured to the outer peripheral wall WA1 with a sidesurface thereof contacting the inner peripheral surface of the innerwall 542 of the inverter unit 530. The module case 611 has, for example,resin molded therein. In the module case 611, the switches 601 and 602,the driver circuits 603, and the capacitor 604 are electricallyconnected together using wires 612. The switch modules 532A are, asdescribed above, attached to the outer peripheral wall WA1 through thespacers 549, but however, FIG. 60 emits the spacers 549 for the brevityof illustration.

In a condition where the switch modules 532A are firmly attached to theouter peripheral wall WA1, a portion of each of the switch modules 532Awhich is closer to the outer peripheral wall WA1, i.e., the coolant path545 is more cooled. In terms of such ease of cooling, the order in whichthe switches 601 and 602, the driver circuits 603, and the capacitor 604are arranged is determined. Specifically, the switches 601 and 602 havethe largest amount of heat generation. The capacitor 604 has anintermediate amount of heat generation. The driver circuits 603 have thesmallest amount of heat generation. Accordingly, the switches 601 and602 are located closest to the outer peripheral wall WA1. The drivercircuits 603 are located farther away from the outer peripheral wallWA1. The capacitor 604 is interposed between the switches 601 and 602and the driver circuit 603. In other words, the switches 601 and 602,the capacitor 604, the driver circuit 603 are arranged in this orderclose to the outer peripheral wall WA1. An area of each of the switchmodules 532A which is attached to the inner wall 542 is preferablysmaller in size than an area of the inner peripheral surface of theinner wall 542 which is contactable with the switch modules 532A.

Although not illustrated in detail, the capacitor modules 532B have thecapacitor 606 disposed in a module case similar in configuration andsize to the switch modules 532A. Each of the capacitor modules 532B is,like the switch modules 532A, secured to the outer peripheral wall WA1with the side surface of the module case 611 placed in contact with theinner peripheral surface of the inner wall 542 of the inverter housing531.

The switch modules 532A and the capacitor modules 532B need notnecessarily be arranged coaxially with each other inside the outerperipheral wall WA1 of the inverter housing 531. For instance, theswitch modules 532A may alternatively be disposed radially inside oroutside the capacitor modules 532B.

When the rotating electrical machine 500 is operating, the switchmodules 532A and the capacitor modules 532B transfer heat generatedtherefrom to the coolant path 545 through the inner wall 542 of theouter peripheral wall WA1, thereby cooling the switch modules 532A andthe capacitor modules 532B.

Each of the electrical modules 532 may be designed to have formedtherein a flow path into which coolant is delivered to cool theelectrical module 532. The cooling structure of the switch modules 532Awill be described below with reference to FIGS. 61(a) and 61(b). FIG.61(a) is a longitudinal sectional view of each of the switch modules532A along a line passing through the outer peripheral wall WA1. FIG.61(b) is a sectional view taken along the line 61B-61B in FIG. 61(a).

Like in FIG. 60, the switch module 532A, as illustrated in FIGS. 61(a)and 61(b), includes the module case 611, the switches 601 and 602 for acorresponding one of the phases of the stator winding 521, the drivercircuits 603, the capacitor 604, and a cooling device made of a pair ofpipes 621 and 622 and the coolers 623. The pipe 621 of the coolingdevice is designed as an inlet pipe through which cooling water isdelivered from the coolant path 545 in the outer peripheral wall WA1 tothe coolers 623. The pipe 622 of the cooling device is designed as anoutlet pipe through which the cooling water is discharged from thecoolers 623 to the coolant path 545. The cooler 623 is prepared for anobject to be cooled. The cooling device may, therefore, be designed tohave a single cooler 623 or a plurality of coolers 623. In the structureshown in FIGS. 61(a) and 61(b), the two coolers 623 are arranged at agiven interval away from each other in a direction perpendicular to thelength of the coolant path 545, in other words, the radial direction ofthe inverter unit 530. The pipes 621 and 622 connect with the coolers623. Each of the coolers 623 has an inner void. Each of the coolers 623may be equipped with inner fins for enhancing the cooling ability.

In the structure equipped with the two coolers 623 which will also bereferred to as a first cooler 623 and a second cooler 623 where thefirst cooler 623 is located closer to the outer peripheral wall WA1 thanthe second cooler 623 is, a first space between the first cooler 623 andthe outer peripheral wall WA1, a second space between the first andsecond coolers 623, and a third space located inside the second cooler623 away from the outer peripheral wall WA1 are locations whereelectrical devices are disposed. The second space, the first space, andthe third space have a higher degree of coolant-cooled capability inthis order. In other words, the second space is a location which has thehighest degree of cooled ability. The first space close to the outerperipheral wall WA1 (i.e., the coolant path 545) is higher in cooledcapability than the third space farther away from the outer peripheralwall WA1. In view of this relation in cooled capability, the switches601 and 602 are arranged in the second space between the first andsecond coolers 623. The capacitor 604 is arranged in the first spacebetween the first cooler 623 and the outer peripheral wall WA1. Thedriver circuits 603 are arranged in the third space located farther awayfrom the outer peripheral wall WA1. Although not illustrated, the drivercircuits 603 may alternatively be disposed in the first space, while thecapacitor 604 may be disposed in the third space.

In either case, in the module case 611, the switches 601 and 602 areelectrically connected to the driver circuits 603 using the wires 612,while the switches 601 and 602 are connected to the capacitor 604 usingthe wires 612. The switches 601 and 602 are located between the drivercircuits 603 and the capacitor 604, so that the wires 612 extending fromthe switches 601 and 602 to the driver circuit 603 are oriented in adirection opposite a direction in which the wires 612 extending from theswitches 601 and 602 to the capacitor 604.

The pipes 621 and 622 are, as can be seen in FIG. 61(b), arrangedadjacent each other in the circumferential direction, that is, from anupstream side to a downstream side of the coolant path 545. The coolingwater, therefore, enters the coolers 623 from the pipe 621 located onthe upstream side and is then discharged from the pipe 622 located onthe downstream side. The stopper 624 is preferably disposed between theinlet pipe 621 and the outlet pipe 621 in the coolant path 545 to stopflow of the cooling water in order to facilitate entry of cooling waterinto the cooling device. The stopper 624 may be designed as a shutter orblock to close the coolant path 545 or an orifice to decrease atransverse sectional area of the coolant path 545.

FIGS. 62(a) to 62(c) illustrate a modified form of the cooling structureof the switch modules 532A. FIG. 62(a) is a longitudinal section of theswitch module 532A along a line traversing the outer peripheral wallWA1. FIG. 62(b) is a sectional view taken along the line 62B-62B in FIG.62(a).

The structure in FIGS. 62(a) and 62(b) has the inlet pipe 621 and theoutlet pipe 622 which are different in layout from those illustrated inFIGS. 62(a) and 62(b). Specifically, the inlet and outlet pipes 621 and622 are arranged adjacent each other in the axial direction. The coolantpath 545, as clearly illustrated in FIG. 62(c), includes an inletsection leading to the inlet pipe 621 and an outlet section leading tothe outlet pipe 622. The inlet section and the outlet section arephysically separate from each other in the axial direction andhydraulically connected through the pipes 621 and 622 and the coolers623.

Each of the switch modules 532A may alternatively be designed to haveone of the following structures.

The structure in FIG. 63(a) is, unlike in FIG. 61(a), equipped with thesingle cooler 263. In the module case 611, space (which will be referredto as a first space) between the cooler 623 and the outer peripheralwall WA1 in the radial direction of the module case 611 has a higherdegree of cooled capability. Space (which will be referred to as asecond space) located inside the cooler 623 farther away from the outerperipheral wall WA1 has a lower degree of cooled capability. In view ofthis relation in cooled capability, the structure in FIG. 63(a) has theswitches 601 and 602 arranged in the first space close to the outerperipheral wall WA1 outside the cooler 623. The capacitor 604 isarranged in the second space located inside the cooler 623. The drivercircuits 603 are disposed farther away from the cooler 623.

Each of the switch modules 532A is, as described above, designed to havethe switches 601 and 602, the driver circuits 603, and the capacitor 604disposed within the module case 611 for one of the phases of the statorwinding 521, but may be modified to have the switches 601 and 602 andthe driver circuits 603 or the capacitor 604 disposed in the module case611 for one of the phases of the stator winding 521.

In FIG. 63(b), the module case 611 has the inlet pipe 621, the outletpipe 622, and the two coolers 623 mounted therein. One of the coolers623 located closer to the outer peripheral wall WA1 will be referred toas a first cooler. One of the coolers 623 located farther away from theouter peripheral wall WA1 will be referred to as a second cooler. Theswitches 601 and 602 are arranged between the first and second coolers623. The capacitor 604 or the driver circuits 603 are arranged close tothe outer peripheral wall WA1 outside the first cooler 623. The switches601 and 602 and the driver circuit 603 are assembled as a singlesemiconductor module which is disposed in the module case 611 along withthe capacitor 604.

In the structure of the switch module 532A illustrated in FIG. 63(b),the capacitor 604 is located outside or inside one of the first andsecond coolers 623 on the opposite side of the one of the first andsecond coolers 623 to the switches 601 and 602. In the illustratedexample, the capacitor 604 is located between the first cooler 623 andthe outer peripheral wall WA1. The switch module 532A may alternativelybe designed to have two capacitors 604 disposed on the both sides of thefirst cooler 623 in the radial direction of the stator winding 521.

The structure in this embodiment delivers cooling water into only theswitch modules 532A other than the capacitor module 532B through thecoolant path 545, but may alternatively be designed to supply thecooling water to both the modules 532A and 532B through the coolant path545.

It is also possible to bring cooling water into direct contact with theelectrical modules 532 to cool them. For instance, the electricalmodules 532 may be, as illustrated in FIG. 64, embedded in the outerperipheral wall WA1 to achieve a direct contact of the outer surface ofthe electrical modules 532 with the cooling water. In this case, each ofthe electrical modules 532 may be partially exposed to the cooling waterflowing in the coolant path 545. Alternatively, the coolant path 545 maybe shaped to have a size increased to be larger than that in FIG. 58 inthe radial direction to arrange the electrical modules 532 fully withinthe coolant path 545. In the case where the electrical modules 532 areembedded in the coolant path 545, the module case 611 of each of theelectrical modules 532 may be equipped with fins disposed in the coolantpath 545, that is, exposed to the cooling water to enhance the abilityto cool the electrical modules 532.

The electrical modules 532, as described above, include the switchmodules 532A and the capacitor modules 532B which are different inamount of heat generation from the switch modules 532A. In terms of sucha difference, it is possible to modify the layout of the electricalmodules 532 in the inverter housing 531 in the following way.

For instance, the switch modules 532A are, as illustrated in FIG. 65,arranged away from each other in the circumferential direction of thestator 520 and located as a whole closer to the upstream side of thecoolant path 545 (i.e., the inlet path 571) than to the downstream side(i.e., the outlet path 572) of the coolant path 545. The cooling waterentering the inlet path 571 is first used to cool the switch modules532A and then used to cool the capacitor modules 532B. In the structureillustrated in FIG. 65, the inlet and outlet pipes 621 and 622 are, likein FIGS. 62(a) and 62(b), arranged adjacent each other in the axialdirection, but however, may be, like in FIGS. 61(a) and 61(b), orientedadjacent each other in the circumferential direction.

The electrical structure of the electrical modules 532 and the bus barmodule 533 will be described below. FIG. 66 is a transverse sectiontaken along the line 66-66 in FIG. 49. FIG. 67 is a transverse sectiontaken along the line 67-67 in FIG. 49. FIG. 68 is a perspective viewwhich illustrates the bus bar module 533. Electrical connections of theelectrical modules 532 and the bus bar module 533 will be discussed withreference to FIGS. 66 to 68.

The inverter housing 531 has the three switch modules 532A (which willalso be referred to below as a first module group) which are, asillustrated in FIG. 66, arranged adjacent each other circumferentiallynext to the bulging portion 573 on the inner wall 542 in which the inletpath 571 and the outlet path 572 are formed in communication with thecoolant path 545. The six capacitor modules 532B are also arrangedcircumferentially adjacent each other next to the first module group. Insummary, the inverter housing 531 has ten regions (i.e., the number ofthe modules 532A and 532B plus one) defined on the inner peripheralsurface of the outer peripheral wall WA1. The ten regions are arrangedadjacent each other in the circumferential direction of the inverterhousing 531. The electrical modules 532 are disposed, one in each ofninth of the regions, while the bulging portion 573 occupies theremaining one of the regions. The three switch modules 532A will also bereferred to as a U-phase module, a V-phase module, and a W-phase module.

Each of the electrical modules 532 (i.e., the switch modules 532A andthe capacitor modules 532B) is, as illustrated in FIGS. 66, 56, and 57,equipped with a plurality of module terminals 615 extending from themodule case 611. The module terminals 615 serve as input/outputterminals through which electrical signals are inputted into oroutputted from the electrical modules 532. The module terminals 615 eachhave a length extending in the axial direction of the inverter housing531. More specifically, the module terminals 615, as can be seen in FIG.51, extend from the module case 611 toward the bottom of the rotorcarrier 511 (i.e., the outside of the vehicle).

The module terminals 615 of the electrical modules 532 are connected tothe bus bar module 533. The switch modules 532A and the capacitormodules 532B are different in number of the module terminals 615 fromeach other. Specifically, each of the switch modules 532A is equippedwith the four module terminals 615, while each of the capacitor modules532B is equipped with the two module terminals 615.

The bus bar module 533, as clearly illustrated in FIG. 68, includes theannular ring 631, the three external terminals 632, and the windingconnecting terminals 633. The external terminals 632 extend from theannular ring 631 and achieve connections with external devices, such asa power supply and an ECU (Electronic Control Unit). The windingconnecting terminals 633 are connected to ends of the phase windings ofthe stator winding 521. The bus bar module 533 will also be referred toas a terminal module.

The annular ring 631 is located radially inside the outer peripheralwall WA1 of the inverter housing 531 and adjacent one of axially opposedends of each of the electrical modules 532. The annular ring 631includes an annular body made from an insulating material, such asresin, and a plurality of bus bars embedded in the annular body. The busbars connect with the module terminals 615 of the electrical modules532, the external terminals 632, and the phase windings of the statorwinding 521, which will be also described later in detail.

The external terminals 632 include the high-potential power terminal632A connecting with a power unit, the low-potential power terminal 632Bconnecting with the power unit, and the single signal terminal 632Cconnecting with the external ECU. The external terminals 632 (i.e., 632Ato 632C) are arranged adjacent each other in the circumferentialdirection of the annular ring 631 and extend in the axial direction ofthe annular ring 631 radially inside the annular ring 631. The bus barmodule 533 is, as illustrated in FIG. 51, mounted in the inverterhousing 531 together with the electrical modules 532. Each of theexternal terminals 632 has an end protruding outside the end plate 547.Specifically, the end plate 547 of the bossed member 543, as illustratedin FIGS. 56 and 57, has the hole 547 a formed therein. The cylindricalgrommet 635 is fit in the hole 547 a. The external terminals 632 passthrough the grommet 635. The grommet 635 also functions as ahermetically sealing connector.

The winding connecting terminals 633 connect with ends of the phasewindings of the stator winding 521 and extend radially outward from theannular ring 631. Specifically, the winding connecting terminals 633include the winding connecting terminal 633U connecting with the end ofthe U-phase winding of the stator winding 521, the winding connectingterminal 633V connecting with the end of the V-phase winding of thestator winding 521, and the winding connecting terminal 633W connectingwith the end of the W-phase winding of the stator winding 521. Each ofthe winding connecting terminals 633 is, as illustrated in FIG. 70, thecurrent sensor 634 which measure an electrical current flowing through acorresponding one of the U-phase winding, the V-phase winding, and theW-phase winding.

The current sensor 634 may be arranged outside the electrical module 532around the winding connecting terminal 633 or installed inside theelectrical module 532.

Connections between the electrical modules 532 and the bus bar module533 will be described below in detail with reference to FIGS. 69 and 70.FIG. 69 is a development view of the electrical modules 532 whichschematically illustrates electrical connections of the electricalmodules 532 with the bus bar module 533. FIG. 70 is a view whichschematically illustrate electrical connections of the electricalmodules 532 arranged in an annular shape with the bus bar module 533. InFIG. 69, power supply lines are expressed by solid lines, while signaltransmission lines are expressed by chain lines. FIG. 70 shows only thepower supply lines.

The bus bar module 533 includes the first bus bar 641, the second busbar 642, and the third bus bars 643 as power supply bus bars. The firstbus bar 641 is connected to the high-potential power terminal 632A. Thesecond bus bar 642 is connected to the low-potential power terminal632B. The three third bus bars 643 are connected to the U-phase windingconnecting terminals 633U, the V-phase winding connecting terminals633V, and the W-phase winding connecting terminals 633W.

The winding connecting terminals 633 and the third bus bars 643 usuallygenerate heat due to the operation of the rotating electrical machine10. A terminal block, not shown, may, therefore, be disposed between thewinding connecting terminals 633 and the third bus bars 643 in contactwith the inverter housing 531 equipped with the coolant path 545.Alternatively, the winding connecting terminals 633 and/or the third busbars 643 may be bent in a crank form to achieve physical contact withthe inverter housing 531 equipped with the coolant path 545.

The above structure serves to release heat generated by the windingconnecting terminals 633 or the third bus bars 643 to cooling waterflowing in the coolant path 545.

FIG. 70 depicts the first bus bar 641 and the second bus bar 642 ascompletely circular bus bars, but however, may alternatively be of aC-shape. Each of the winding connecting terminals 633U, 633V, and 633Wmay alternatively be connected directly to a corresponding one of theswitch modules 532A (i.e., the module terminals 615) without use of thebus bar module 533.

Each of the switch modules 532A is equipped with the four moduleterminals 615 including a positive terminal, a negative terminal, awinding terminal, and a signal terminal. The positive terminal isconnected to the first bus bar 641. The negative terminal is connectedto the second bus bar 642. The winding terminal is connected to one ofthe third bus bars 643.

The bus bar module 533 is also equipped with the fourth bus bars 644 assignal transmission bus bars. The signal terminal of each of the switchmodules 532A is connected to one of the fourth bus bars 644. The fourthbus bar 644 are connected to the signal terminal 632C.

In this embodiment, each of the switch modules 532A receives a controlsignal transmitted from an external ECU through the signal terminal632C. Specifically, the switches 601 and 602 in each of the switchmodules 532A are turned on or off in response to the control signalinputted through the signal terminal 632C. Each of the switch modules532A is, therefore, connected to the signal terminal 632C withoutpassing through a control device installed in the rotating electricalmachine 500. The control signals may alternatively be, as illustrated inFIG. 71, produced by the control device of the rotating electricalmachine 500 and then inputted to the switch modules 532A.

The structure of FIG. 71 has the control board 651 on which the controldevice 652 is mounted. The control device 652 is connected to the switchmodules 532A. The signal terminal 632C is connected to the controldevice 652. For instance, an external ECU serving as a host controldevice outputs a command signal associated with the motor mode or thegeneration mode to the control device 652. The control device 652 thencontrols on-off operations of the switches 601 and 602 of each of theswitch modules 532A.

In the inverter unit 530, the control board 651 may be arranged closerto the outside of the vehicle (i.e., the bottom of the rotor carrier511) than the bus bar module 533 is. The control board 651 mayalternatively be disposed between the electrical modules 532 and the endplate 547 of the bossed member 543. The control board 651 may be locatedto overlap at least a portion of each of the electrical modules 532 inthe axial direction.

Each of the capacitor modules 532B is equipped with two module terminals615 serving as a positive terminal and a negative terminal. The positiveterminal is connected to the first bus bar 641. The negative terminal isconnected to the second bus bar 642.

Referring back to FIGS. 49 and 50, the inverter housing 531 has disposedtherein the bulging portion 573 which is equipped with the inlet path571 and the outlet path 572 for cooling water. The inlet path 571 andthe outlet path 572 are aligned with the electrical modules 532 arrangedadjacent each other in the circumferential direction of the inverterhousing 531. The external terminals 632 are arranged adjacent thebulging portion 573 in the radial direction of the inverter housing 531.In other words, the bulging portion 573 and the external terminals 632are located at the same angular position in the circumferentialdirection of the inverter housing 531. In this embodiment, the externalterminals 632 are disposed radially inside the bulging portion 573. Asthe inverter housing 531 is viewed from inside the vehicle, theinlet/outlet port 574 and the external terminals 632 are, as clearlyillustrated in FIG. 48, aligned with each other in the radial directionof the end plate 547 of the bossed member 543.

The bulging portion 573 and the external terminals 632 are, as clearlyillustrated in FIG. 66, arranged adjacent the electrical modules 532 inthe circumferential direction, thereby enabling the inverter unit 530 tobe reduced in size, which also enables the rotating electrical machine500 to be reduced in size.

Referring back to the structure of the tire wheel assembly 400 in FIGS.45 and 47, the cooling pipe H2 is joined to the inlet/outlet port 574.The electrical cable H1 is joined to the external terminals 632. Theelectrical cable H1 and the cooling pipe H2 are arranged inside thestorage duct 440.

In the inverter housing 531, the three switch modules 532A are arrangedadjacent each other next to the external terminals 632 in thecircumferential direction. The six capacitor modules 532B are arrangednext to the array of the switch modules 532A in the circumferentialdirection. Such layout may be modified in the following way. Forinstance, the array of the three switch modules 532A may be arranged ata location farthest away from the external terminals 632, that is,diametrically opposed to the external terminals 632 across the rotatingshaft 501. Alternatively, the switch modules 532A may be arranged at anincreased interval away from each other in the circumferentialdirection, so that the capacitor modules 532B may be disposed betweenthe switch modules 532A.

The layout of the switch modules 532A located farthest away from theexternal terminals 632, that is, diametrically opposed to the externalterminals 632 across the rotating shaft 501 minimizes a risk of failurein operation of the switch modules 532A caused by mutual inductancebetween the external terminals 632 and the switch modules 532A.

Next, the structure of the resolver 660 working as an angular positionsensor will be described below.

The inverter housing 531, as illustrated in FIGS. 49 to 51, has disposedtherein the resolver 660 which measures the electrical angle θ of therotating electrical machine 500. The resolver 660 functions as anelectromagnetic induction sensor and includes the resolver rotor 661secured to the rotating shaft 501 and the resolver stator 662 whichradially faces an outer circumference of the resolver rotor 661. Theresolver rotor 661 is made of a ring-shaped disc fit on the rotatingshaft 501 coaxially with the rotating shaft 501. The resolver stator 662includes the circular stator core 663 and the stator coil 664 woundaround teeth of the stator core 663. The stator coil 664 includes asingle-phase exciting coil and two-phase output coils.

The exciting coil of the stator coil 664 is energized by a sine waveexcitation signal to generate magnetic flux which interlinks with theoutput coils. This causes a positional relation of the exciting coilwith the two output coils to be changed cyclically as a function of anangular position of the resolver rotor 661 (i.e., a rotation angle ofthe rotating shaft 501), so that the number of magnetic fluxesinterlining with the output coils is changed cyclically. In thisembodiment, the exciting coil and the output coils are arranged so thatvoltages, as developed at the output coils, are out of phase by π/2.Output voltage generated by the output coils will, therefore, be wavesderived by modulating the excitation signal with modulating waves sin θand cos θ. Specifically, if the excitation signal is expressed by sinΩt, the modulated waves will be sin θ×sin Ωt and cos θ×sin Ωt.

The resolver 660 is equipped with a resolver digital converter. Theresolver digital converter works to perform wave detection using themodulated wave and the excitation signal to calculate the electricalangle θ. For instance, the resolver 660 is connected to the signalterminal 632C. An output of the resolver digital converter is inputtedto an external device through the signal terminal 632C. In a case wherea control device is installed in the rotating electrical machine 500,the output of the resolver digital converter is inputted to the controldevice.

The structure of the resolver 660 installed in the inverter housing 531will be described below.

The bossed member 543 of the inverter housing 531, as illustrated inFIGS. 49 and 51, has formed thereon the hollow cylindrical boss 548. Theboss 548 has the protrusion 548 a formed on an inner periphery thereofin the shape of an inner shoulder. The protrusion 548 a projects in adirection perpendicular to the axial direction of the inverter housing531. The resolver stator 662 is secured using screws in contact with theprotrusion 548 a. In the boss 548, the bearing 650 is arranged on anopposite side of the protrusion 548 a to the resolver 660.

Within the boss 548, the housing cover 666 is arranged on an oppositeside of the resolver 660 to the protrusion 548 a in the axial direction.The housing cover 666 is made of an annular ring shaped disc and closesan inner chamber of the boss 548 in which the resolver 660 is disposed.The housing cover 666 is made from an electrically conductive material,such as a carbon fiber reinforced plastic (CFRP). The housing cover 666has formed in the center thereof the center hole 666 a through which therotating shaft 501 passes. The center hole 666 a, as clearly illustratedin FIG. 49, has disposed therein the sealing member 667 whichhermetically seal an air gap between the center hole 666 a and the outerperiphery of the rotating shaft 501. The sealing member 667 hermeticallyseals the inner chamber of the boss 548 in which the resolver 660 isdisposed. The sealing member 667 may be designed as a slidable seal madefrom resin.

The inner chamber in which the resolver 660 is disposed is surrounded ordefined by the annular boss 548 of the bossed member 543 and which hasaxially-opposed ends closed by the bearing 560 and the housing cover666. The outer circumference of the resolver 660 is, therefore,surrounded by the conductive material, thereby minimizing adverseeffects of electromagnetic noise on the resolver 660.

The inverter housing 531 is, as described above in FIG. 57, designed tohave a double-walled structure equipped with the outer peripheral wallWA1 and the inner peripheral wall WA2. The stator 520 is arrangedradially outside the outer peripheral wall WA1. The electrical modules532 are arranged between the outer peripheral wall WA1 and the innerperipheral wall WA2. The resolver 660 is disposed radially inside theinner peripheral wall WA2. The inverter housing 531 is made fromconductive material. The stator 520 and the resolver 660 are, therefore,isolated from each other through a conductive wall (i.e., a conductivedouble wall), that is, the outer peripheral wall WA1 and the innerperipheral wall WA2, thereby minimizing a risk of magnetic interferencebetween the stator 520 (i.e., the magnetic circuit) and the resolver660.

The rotor cover 670 which is arranged in the open end of the rotorcarrier 511 will be described below in detail.

The rotor carrier 511, as illustrated in FIGS. 49 and 50, has the endopen in the axial direction. The rotor cover 670 which is made of asubstantially ring-shaped disc is disposed on the open end, i.e.,partially covers the open end. The rotor cover 670 is secured to therotor carrier 511 using, for example, welding techniques or vises (i.e.,screws). The rotor cover 670 is preferably shaped to have a portionsmaller in size (i.e. diameter) than the inner periphery of the rotorcarrier 511 to hold the magnet unit 512 from moving in the axialdirection. The rotor cover 670 has an outer diameter identical with thatof the rotor carrier 511, but has an inner diameter slightly greaterthan an outer diameter of the inverter housing 531. The outer diameterof the inverter housing 531 is equal to the inner diameter of the stator520.

The stator 520 is, as described above, attached to the outercircumference of the inverter housing 531. Specifically, the stator 520and the inverter housing 531 joined together. The inverter housing 531has a portion protruding in the axial direction from the joint of thestator 520 and the inverter housing 531. Such a protrusion of theinverter housing 531 is, as clearly illustrated in FIG. 49, surroundedby the rotor cover 670. The sealing member 671 is disposed between theinner circumference of the rotor cover 670 and the outer periphery ofthe inverter housing 531 to hermetically seal an air gap therebetween.The sealing member 671, therefore, hermetically closes an inner chamberof the rotor cover 670 in which the magnet unit 512 and the stator 520are disposed. The sealing member 671 may be made of a slidable seal madefrom resin.

The above embodiment offers the following beneficial advantages.

The rotating electrical machine 500 has the outer peripheral wall WA1 ofthe inverter housing 531 arranged radially inside the magnetic circuitmade up of the magnet unit 512 and the stator winding 521 and also hasthe coolant path 545 formed in the outer peripheral wall WA1. Therotating electrical machine 500 also has the plurality of electricalmodules 532 arranged along the inner circumference of the outerperipheral wall WA1. This enables the magnetic circuit, the coolant path545, and the power converter to be arranged in a stacked shape in theradial direction of the rotating electrical machine 500, therebypermitting an axial dimension of the rotating electrical machine 500 tobe reduced and also achieving effective layout of parts in the rotatingelectrical machine 500. The rotating electrical machine 500 also ensuresthe stability in cooling the electrical modules 532 composing the powerconverter, thereby enabling the rotating electrical machine 500 tooperate with high efficiency and to be reduced in size thereof.

The electrical modules 532 (i.e., the switch modules 532A and thecapacitor modules 532B) equipped with heat generating devices, such assemiconductor switches or capacitors are placed in direct contact withthe inner peripheral surface of the outer peripheral wall WA1, therebycausing heat, as generated by the electrical modules 532, to betransferred to the outer peripheral wall WA1, so that the electricalmodules 532 are well cooled.

In each of the switch modules 532A, the coolers 623 are disposed outsidethe switches 601 and 602. In other words, the switches 601 and 602 arearranged between the coolers 623. The capacitor 604 is placed on anopposite side of at least one of the coolers 623 to the switches 601 and602, thereby enhancing the cooling of the capacitor 604 as well as theswitches 601 and 602.

In each of the switch modules 532A, the coolers 623 are, as describedabove, placed on both sides of the switches 601 and 602. The drivercircuit 603 is arranged on an opposite side of at least one of thecoolers 623 to the switches 601 and 602, while the capacitor 604 isarranged on the other opposite side of the cooler 623, thereby enhancingthe cooling of the driver circuit 603 and the capacitor 604 as well asthe switches 601 and 602.

For instance, each of the switch modules 532A is designed to have thecoolant path 545 which delivers cooling water into the modules to coolthe semiconductor switches. Specifically, each module 532A is cooled bythe outer peripheral wall WA1 through which the cooling water passes andalso by the cooling water flowing in the module 532A. This enhances thecooling of the switch modules 532A.

The rotating electrical machine 500 is equipped with a cooling system inwhich cooling water is delivered into the coolant path 545 from theexternal circulation path 575. The switch modules 532A are placed on anupstream side of the coolant path 545 close to the inlet path 571, whilethe capacitor modules 532B are arranged downstream of the switch modules532A. Generally, the cooling water flowing through the coolant path 545has a lower temperature on the upstream side than the downstream side.The switch modules 532A are, therefore, cooled better than the capacitormodules 532B.

The electrical modules 532 are, as described above, arranged at shorterintervals (i.e., the first intervals INT1) or a longer interval (i.e.,the second interval INT2) away from each other in the circumferentialdirection of the rotating electrical machine 500. In other words, theintervals between the electrical modules 532 include a single longerinterval (i.e., the second interval INT2). The bulging portion 573 whichis equipped with the inlet path 571 and the outlet path 572 lies in thelonger interval. These arrangements enable the inlet path 571 and theoutlet path 572 of the coolant path 545 to be arranged radially insidethe outer peripheral wall WA1. Usually, it is required to increase thevolume or flow rate of cooling water in order to enhance the coolingefficiency. Such a requirement may be met by increasing an area of anopening of each of the inlet path 571 and the outlet path 572. This isachieved in this embodiment by placing the bulging portion 573 in thelonger interval (i.e., the second interval INT2) between the electricalmodules 532, which enables the inlet path 571 and the outlet path 572 tobe shaped to have required sizes.

The external terminals 632 of the bus bar module 533 are arrangedadjacent the bulging portion 573 in the radial direction of the rotor510 radially inside the outer peripheral wall WA1. In other words, theexternal terminals 632 is placed together with the bulging portion 573within the larger interval (i.e., the second interval INT2) between theelectrical modules 532 arranged adjacent each other in thecircumferential direction of the rotor 510. This achieves a suitablelayout of the external terminals 632 without physical interference withthe electrical modules 532.

The outer-rotor type rotating electrical machine 500 is, as describedabove, engineered to have the stator 520 attached to the radially outercircumference of the outer peripheral wall WA1 and also have theplurality of electrical modules 532 arranged radially inside the outerperipheral wall WA1. This layout causes heat generated by the stator 520to be transferred to the outer peripheral wall WA1 from radially outsideand also causes heat generated by the electrical modules 532 to betransferred to the outer peripheral wall WA1 from radially inside. Thestator 520 and the electrical modules 532 are simultaneously cooled bycooling water flowing through the coolant path 545, thereby facilitatingdissipation of thermal energy generated by heat-producing partsinstalled in the rotating electrical machine 500.

The electrical modules 532 arranged radially inside the outer peripheralwall WA1 and the stator winding 521 arranged radially outside the outerperipheral wall WA1 are electrically connected together using thewinding connecting terminals 633 of the bus bar module 533. The windingconnecting terminals 633 are disposed away from the coolant path 545 inthe axial direction of the rotating electrical machine 500. Thisfacilitates electrical connections of the electrical modules 532 to thestator winding 521 even in a structure in which the coolant path 545extends in an annular form in the outer peripheral wall WA1, in otherwords, the outside and the inside of the outer peripheral wall WA1 areisolated from each other by the coolant path 545.

The rotating electrical machine 500 in this embodiment is designed tohave a decreased size of teeth or no teeth (i.e., iron cores) betweenthe conductors 523 of the stator 520 arranged adjacent each other in thecircumferential direction to reduce a limitation on a torque outputwhich results from magnetic saturation occurring between the conductors532. The rotating electrical machine 500 also has the conductors 523 ofa thin flat shape to enhance a degree of torque output. This structureenables a region radially inside the magnetic circuit to be increased insize by reducing the thickness of the stator 520 without altering theouter diameter of the rotating electrical machine 500. The region isused to have the outer peripheral wall WA1 equipped with the coolantpath 545 disposed therein and enables the electrical modules 532 to beplaced radially inside the outer peripheral wall WA1.

The rotating electrical machine 500 is equipped with the magnet unit 512in which magnet-produced magnetic fluxes are concentrated on the d-axisto enhance a degree of output torque. Such a structure of the magnetunit 512 enables a radial thickness thereof to be reduced and the regionradially inside the magnetic circuit to be, as described above,increased in volume thereof. The region is used to have the outerperipheral wall WA1 with the coolant path 545 disposed therein and alsohave the plurality of electrical modules 532 to be placed radiallyinside the outer peripheral wall WA1. The region also be used to havethe bearing 560 and the resolver 660 arranged therein in addition to themagnetic circuit, the outer peripheral wall WA1, and the electricalmodules 532.

The tire wheel assembly 400 using the rotating electrical machine 500 asan in-wheel motor is attached to the vehicle body using the base plate405 secured to the inverter housing 531 and a mount mechanism, such assuspensions. The rotating electrical machine 500 is designed to have areduced size, thus occupying a decreased size of space in the vehiclebody. This enables the volume of space required for installation of apower unit, such as a storage battery in the vehicle or the volume of apassenger compartment of the vehicle to be increased.

Modified forms of the in-wheel motor will be described below.

First Modification of in-Wheel Motor

The rotating electrical machine 500 has the electrical modules 532 andthe bus bar module 533 arranged radially inside the outer peripheralwall WA1 of the inverter unit 530 and also has the stator 520 arrangedradially outside the outer peripheral wall WA1. Locations of the bus barmodules 533 relative to the electrical modules 532 are optional. Thephase windings of the stator winding 521 may be connected to the bus barmodule 533 radially across the outer peripheral wall WA1 using windingconnecting wires (e.g., the winding connecting terminals 633) whoselocations are optional.

For example, the bus bar module 533 or the winding connecting wires maybe arranged in the following layouts.

(a1) The bus bar module 533 may be located closer to the outer side ofthe vehicle, that is, the bottom of the rotor carrier 511 than theelectrical modules 532 are in the axial direction of the rotatingelectrical machine 500.(a2) The bus bar module 533 may be located closer to the inner side ofthe vehicle, that is, farther away from the rotor carrier 511 than theelectrical modules 532 is in the axial direction.

The winding connecting wires may be placed on the following location.

(β1) The winding connecting wires may be arranged close to the outerside of the vehicle, that is, the bottom of the rotor carrier 511 in theaxial direction of the rotating electrical machine 500.(β2) The winding connecting wires may be located closer to the innerside of the vehicle, that is, far away from the rotor carrier 511.

Four types of locations of the electrical modules 532, the bus barmodule 533, and the winding connecting wires will be described belowwith reference to FIGS. 72(a) to 72(d). FIGS. 72(a) to 72(d) arelongitudinal sectional views which partially illustrate modified formsof the rotating electrical machine 500. The same reference numbers asemployed in the above embodiments refer to the same parts, andexplanation thereof in detail will be omitted here. The windingconnecting wires 637 are electrical conductors connecting of the phasewindings of the stator winding 521 with the bus bar module 533 andcorrespond to the above described winding connecting terminals 633.

In the structure illustrated in FIG. 72(a), a locational relation of thebus bar module 533 to the electrical modules 532 corresponds to theabove described layout (a1). The winding connecting wires 637 arearranged in the above layout (β1). Specifically, connections of theelectrical modules 532 to the bus bar module 533 and connections of thestator winding 521 to the bus bar module 533 are made on the outer sideof the vehicle (i.e., close to the bottom of the rotor carrier 511).This layout is identical with that in FIG. 49.

The structure in 72(a) enables the coolant path 545 to be formed in theouter peripheral wall WA1 without any physical interference with thewinding connecting wires 637 and also facilitates the layout of thewinding connecting wires 637 connecting the stator winding 521 and thebus bar module 533 together.

In the structure illustrated in FIG. 72(b), a locational relation of thebus bar module 533 to the electrical modules 532 corresponds to theabove described layout (a1). The winding connecting wires 637 arearranged in the above layout (β2). Specifically, connections of theelectrical modules 532 to the bus bar module 533 are made on the outerside of the vehicle (i.e., close to the bottom of the rotor carrier 511,while the stator winding 521 and the bus bar module 533 are connectedclose to the inner side of the vehicle (i.e., far away from the rotorcarrier 511).

The structure in FIG. 72(b) enables the coolant path 545 to be formed inthe outer peripheral wall WA1 without any physical interference with thewinding connecting wires 637.

In the structure illustrated in FIG. 72(c), a locational relation of thebus bar module 533 to the electrical modules 532 corresponds to theabove described layout (a2). The winding connecting wires 637 arearranged in the above layout (β1). Specifically, connections of theelectrical modules 532 to the bus bar module 533 are made on the innerside of the vehicle (i.e., far away from the bottom of the rotor carrier511, while the stator winding 521 and the bus bar module 533 areconnected close to the outer side of the vehicle (i.e., close to therotor carrier 511).

In the structure illustrated in FIG. 72(d), a locational relation of thebus bar module 533 to the electrical modules 532 corresponds to theabove described layout (a2). The winding connecting wires 637 arearranged in the above layout (β2). Specifically, connections of theelectrical modules 532 to the bus bar module 533 and connections of thestator winding 521 to the bus bar module 533 are made on the inner sideof the vehicle (i.e., far away from the bottom of the rotor carrier511).

The structure in FIG. 72(c) or 72(d) in which the bus bar module 533 isarranged farther away from the rotor carrier 511 than the electricalmodules 532, thereby facilitating layout of electrical wires leading to,for example, an electrical device, such as a fan motor, if installed inthe rotor carrier 511. The structure also enables the bus bar module 533to be placed close to the resolver 660 mounted closer to the inner sideof the vehicle than the bearings 563 are, thereby facilitating layout ofelectrical wires leading to the resolver 660.

Second Modification of in-Wheel Motor

Modified forms of a mount structure of the resolver rotor 661 will bedescribed below. Specifically, the rotating shaft 501, the rotor carrier511, and the inner race 561 of the bearing 560 are rotated together inthe form of a rotating unit. The structure in which the resolver rotor611 is mounted to the rotating unit will be described below.

FIGS. 73(a) to 73(c) are structural views which illustrate modificationsof the mount structure for attaching the resolver rotor 661 to therotating unit. In any of the modifications, the resolver 660 is arrangedwithin a hermetically sealed space which is surrounded by the rotorcarrier 511 and the inverter housing 531 and protected from splashing ofwater or mud. FIG. 73(a) shows the same structure of the bearing 560 asthat in FIG. 49. The structures in FIGS. 73(b) and 73(c) have thebearing 560 which is different in structure from that illustrated inFIG. 49 and arranged away from the end plate 514 of the rotor carrier511. FIGS. 73(a) to 73(c) each demonstrate two available locations wherethe resolver rotor 661 is mounted. Although not clearly illustrated, theboss 548 of the bossed member 543 may be extended to or near the outercircumference of the resolver rotor 661 to have the resolver stator 662secured to the boss 548.

In the structure illustrated in FIG. 73(a) the resolver rotor 661 isattached to the inner race 561 of the bearing 560. Specifically, theresolver rotor 661 is secured to a surface of the flange 561 b of theinner race 561 which faces in the axial direction or an end surface ofthe cylinder 561 a of the inner race 561 which faces in the axialdirection.

In the structure illustrated in FIG. 73(b), the resolver rotor 661 isattached to the rotor carrier 511. Specifically, the resolver rotor 661is secured to an inner peripheral surface of the end plate 514 of therotor carrier 511. The rotor carrier 511 has the hollow cylinder 515extending from an inner circumferential edge of the end plate 514 alongthe rotating shaft 501. The resolver rotor 661 may alternatively besecured to an outer periphery of the cylinder 515 of the rotor carrier511. In the latter case, the resolver rotor 661 is disposed between theend plate 514 of the rotor carrier 511 and the bearing 560.

In the structure illustrated in FIG. 73(c), the resolver rotor 661 isattached to the rotating shaft 501. Specifically, the resolver rotor 661is mounted on the rotating shaft 501 between the end plate 514 of therotor carrier 511 and the bearing 560 or on the opposite side of thebearing 560 to the rotor carrier 511.

Third Modification of in-Wheel Motor

Modifications of the structures of the inverter housing 531 and therotor cover 670 will be described below with reference to 74(a) and74(b) which are longitudinal sectional view schematically illustratingthe structure of the rotating electrical machine 500. The same referencenumber as employed in the above embodiments refer to the same parts. Thestructure in FIG. 74(a) substantially corresponds to that illustrated inFIG. 49. The structure in FIG. 74(b) substantially corresponds to apartially modified form of that in 74(a).

In the structure illustrated in FIG. 74(a), the rotor cover 670 securedto an open end of the rotor carrier 511. The rotor cover 670 surroundsthe outer peripheral wall WA1 of the inverter housing 531. In otherwords, the rotor cover 670 has an inner circumferential end surfacefacing the outer peripheral surface of the outer peripheral wall WA1.The sealing member 671 is disposed between the inner circumferential endsurface of the rotor cover 670 and the outer peripheral surface of theouter peripheral wall WA1. The housing cover 666 is disposed inside theboss 548 of the inverter housing 531. The sealing member 667 is disposedbetween the housing cover 666 and the rotating shaft 501. The externalterminals 632 of the bus bar module 533 extend through the wall of theinverter housing 531 downward, as viewed in FIG. 74(a).

The inverter housing 531 has formed therein the inlet path 571 and theoutlet path 572 which communicate with the coolant path 545. Theinverter housing 531 has also formed thereon the inlet/outlet port 574in which open ends of the inlet path 571 and the outlet path 572 lie.

In the structure illustrated in FIG. 74(b), the inverter housing 531(i.e., the bossed member 543) has the annular protrusion 681 formedthereon in the shape of a flange. The annular protrusion 681 extendssubstantially parallel to the rotating shaft 501 inwardly in theinverter housing 531 (i.e., in the vehicle). The rotor cover 670surrounds the protrusion 681 of the inverter housing 531. In otherwords, the rotor cover 670 has an inner end surface facing the outerperiphery of the protrusion 681. The sealing member 671 is interposedbetween the inner end surface of the rotor cover 670 and the outerperiphery of the protrusion 681. The external terminals 632 of the busbar module 533 extend through the wall of the boss 548 of the inverterhousing 531 into the inner space of the boss 548 and also pass throughthe wall of the housing cover 666 toward the inside of the vehicle(downward, as viewed in FIG. 74(b)).

The inverter housing 531 has formed therein the inlet path 571 and theoutlet path 572 which communicate with the coolant path 545. The inletpath 571 and the outlet path 572 extend to the inner periphery of theboss 548 and then connect with the connecting pipes 682 which extendinwardly through the wall of the housing cover 666 (i.e. downward asviewed in FIG. 74(b)). Portion of the pipes 682 extending inside thehousing cover 666 (i.e., toward the inside of the vehicle) serve as theinlet/outlet port 574.

The structure in FIG. 74(a) or 74(b) hermetically seals the inner spaceof the rotor carrier 511 and the rotor cover 670 and achieves smoothrotation of the rotor carrier 511 and the rotor cover 670 relative tothe inverter housing 531.

Particularly, the structure in FIG. 74(b) is designed to have the rotorcover 670 which is smaller in inner diameter than that in FIG. 74(a).The inverter housing 531 and the rotor cover 670 are, therefore, laid tooverlap each other in the axial direction of the rotating shaft 501inside the electrical modules 532 in the vehicle, thereby minimizing arisk of adverse effects of electromagnetic noise in the electricalmodules 532. The decreased inner diameter of the rotor cover 670 resultsin a decrease in diameter of a sliding portion of the sealing member671, thereby reducing mechanical loss of rotation of the slidingportion.

Fourth Modification of in-Wheel Motor

A modification of the structure of the stator winding 521 will bedescribed below with reference to FIG. 75.

The stator winding 521 is, as clearly illustrated in FIG. 75, made ofconductors which are shaped to have a rectangular transverse section andwave-wound with a long side thereof extending in the circumferentialdirection of the stator winding 521. Each of the three-phase conductors532 of the stator winding 521 has coil ends and coil sides. The coilsides are arranged at a given interval away from each other andconnected together by the coil ends. The coil sides of the conductors523 which are arranged adjacent each other in the circumferentialdirection of the stator winding 521 have side surfaces which face in thecircumferential direction and placed in contact with each other or at asmall interval away from each other.

The coil ends of each of the phase windings of the stator winding 521are bent in the radial direction. Specifically, the stator winding 521(i.e., the conductors 523) is bent inwardly in the radial direction atlocations which are different among the U-, V-, and W-phase windings andaway from each other in the axial direction, thereby avoiding physicalinterference with each other. In the illustrated structure, the coilends of the conductors 523 of the U-, V-, and W-phase windings are, asdescribed above, bent at right angles inwardly in the radial directionof the stator winding 521 at locations axially offset from each other bya distance equivalent to the thickness of the conductors 523. The coilsides of the conductors 523 which are arranged adjacent each other inthe circumferential direction have lengths which extend in the axialdirection and are preferably identical with each other.

The production of the stator 520 in which the stator core 522 isinstalled in the stator winding 521 may be achieved by preparing thehollow cylindrical stator winding 521 which has a slit to make endsurfaces facing in the circumferential direction, in other words, tomake the stator winding 521 in a substantially C-shape, fitting thestator core 522 inside an inner periphery of the stator winding 521, andthen joining the facing end surfaces to complete the stator winding 521of a complete hollow cylindrical shape.

Alternatively, the stator 520 may be produced by preparing the statorcore 522 made of three discrete core sections arranged adjacent eachother in the circumferential direction and then placing the coresections inside the inner periphery of the hollow cylindrical statorwinding 521.

Other Modifications

The rotating electrical machine 500 is, as illustrated in FIG. 50,designed to have the inlet path 571 and the outlet path 572 of thecoolant path 545 which are collected in one place. This layout may bemodified in the following way. For instance, the inlet path 571 and theoutlet path 572 may be placed at locations separate from each other inthe circumferential direction of the rotating electrical machine 500.Specifically, the inlet path 571 and the outlet path 572 may be arrangedat an angular interval of 180° away from each other in thecircumferential direction, in other words, diametrically opposed to eachother. At least one of the inlet path 571 and the outlet path 572 may bemade up of a plurality of discrete paths.

The tire wheel assembly 400 in this embodiment is designed to have therotating shaft 501 protruding in one of axially opposite directions ofthe rotating electrical machine 500, but however, the rotating shaft 501may alternatively have end portions protruding both in the axialopposite directions. This is suitable for vehicles equipped with asingle front or a single rear wheel.

The rotating electrical machine 500 may alternatively be designed tohave an inner rotor-structure for use in the tire wheel assembly 400.

Fifteenth Modification

The fifteenth modification is a modified form of the structure of therotor in the above embodiments. The following discussion will refer onlyto parts of the rotating electrical machine which are different fromthose in the above embodiments and modifications. The rotatingelectrical machine in this modification has substantially the samestructure as in the first embodiment.

The fifteenth modification is equipped with the magnet holder 41 and themagnet unit 42 which have structures illustrated in FIGS. 76 to 80(b).FIGS. 76 to 80(b) illustrate the rotor 40 which is, like in the firstembodiment, installed in an outer rotor rotating electrical machine. Therotor 40 is, like in the first embodiment, disposed radially outside thestator 50 to be rotatable and faces the stator in the radial direction.The rotor 40 is designed as an IPM rotor and equipped with the magnetunit 700 and the rotor core 701 serving as a magnetic field-producingcore.

The magnet unit 700 includes a plurality of magnets 702 arrangedadjacent each other in the circumferential direction of the rotor 40.Each of the magnets 702 is magnetically oriented, as already describedwith reference to FIG. 9 or 30, to have a polar anisotropic structureand has easy axes of magnetization which, as indicated by a broken line,extend in an arc shape between the d-axis (i.e., the center of amagnetic pole) and the q-axis (i.e., a boundary between magnetic poles).The easy axes of magnetization define arc-shaped magnet-producedmagnetic paths.

More specifically, each of the magnets 702 has a plurality ofmagnet-produced magnetic paths which, as clearly illustrated in FIG. 77,extend in a circular arc-shape around a center point defined on theq-axis. The magnet-produced magnetic paths includes a magnetic pathextending on a circular arc OA (which will also be referred to as amagnetically-oriented circular arc) which is defined to extend about thecenter point and pass through the first intersection P1 between thed-axis and a side surface (which will also be referred to as a nearstator outer surface (i.e. a near armature peripheral surface) of themagnet 702. The magnetically-oriented circular arc OA is preferablydefined to have a tangent line on the first intersection P1 whichbecomes more parallel to the d-axis as approaching the d-axis.

The magnet-produced magnetic path extending along themagnetically-oriented circular arc OA is the longest among all themagnet-produced magnetic paths in each of the magnets 702. The fartheraway from the magnetically-oriented circular arc OA, the shorter themagnet-produced magnetic paths in each of the magnets 702. For instance,in a region close to the q-axis in each of the magnets 702, themagnet-produced magnetic path, as indicated by a broken line, locatedclose to the stator 50 is shorter than that located further from thestator 50, while in a region close to the d-axis in each of the magnets702, the magnet-produced magnetic path located away from the stator 50is shorter than that located closer to the stator 50.

The magnet-produced magnetic paths (i.e., the magnetically-orientedcircular arc OA) may be shaped to have a portion of a true circle or anoval. The center of the arc OA is, as described above, defined on theq-axis, but may be offset from the q-axis. The center of the arc OA ispreferably located closer to the q-axis than to the d-axis.

The magnet unit 700 has every two of the magnets 702 which are arrangedadjacent each other in the circumferential direction and have directionsof magnetization oriented in opposite directions, so that differentpolarities are arranged alternately in the circumferential direction.

Each of the magnets 702 is shaped to have a rectangular transverssection, as viewed in the axial direction of the magnet unit 700. Eachof the magnets 702 is magnetically oriented to be symmetrical withrespect to the d-axis between a respective adjacent two of the q-axes.Each of the magnets 702 has a length extending perpendicular to thed-axis.

The rotor 4 in this modification includes the rotor core 701 instead ofthe cylinder 43 in the first embodiment. The rotor core 701 is securedto an outer edge of the intermediate portion 45. The rotor core 701 isof a hollow cylindrical shape whose center lies on the rotating shaft11. The rotor core 701 has an outer diameter identical with that of theintermediate portion 45. The rotor core 701 is disposed radially outsidethe stator 50 and faces the stator winding 51 in the radial direction ofthe stator 50.

The rotor core 701 has formed therein a plurality of magnet chambers 703arranged at a constant interval away from each other in thecircumferential direction. The magnets 702 are mounted in the magnetchamber 703 and, as described above, have directions of magnetizationdifferent between magnetic poles arranged adjacent each other in thecircumferential direction.

More specifically, the rotor core 701 includes the hollow cylindricalouter wall 704, the hollow cylindrical inner wall 705 arranged radiallyinside the outer wall 704, and the dividing walls 706 extending in theradial direction to connect the outer wall 704 and the inner wall 705together.

The magnet chamber 703 are spaces which are surrounded by the outer wall704, the inner wall 705, and the dividing walls 706 and extend throughthe rotor core 701 in the axial direction. The magnet chambers 703 areisolated from each other by the dividing walls 706 in thecircumferential direction. The dividing walls 706 extend along theq-axes in the radial direction.

The rotor core 701 is made from a soft magnetic material. The outer wall704 functions as a back yoke. The rotor core 701 is, as can be seen inFIG. 78, made of a ring-shaped stack of a plurality of annular softmagnetic core sheets, i.e., the magnetic steel plates 701 a. Each of themagnetic steel plates 701 a is of a flat plate shape.

Generally, when a rotor core is made by stacking magnetic steel plateson each other, such a stack is gripped or compressed in the axialdirection using rivets or bolts. The magnetic steel plates are usuallythin. Firmly compressing the stack of the magnetic steel plates directlyusing rivets or bolts, therefore, will result in a risk that stress mayconcentrate on contacts between the rivets or bolts and the magneticsteel plates, so that the magnetic steel plates are undesirably deformedor broken. In a case where the rotating electrical machine is used invehicles, it may cause physical impact or vibration to act on themagnetic steel plate, so that stress may concentrate locally on thecontacts between the rivets or bolts and the magnetic steel plates, thusresulting in breakage or deformation thereof.

In order to alleviate the above problem, the fifteenth modification isdesigned to grip or compress the stack of the magnetic steel plates 701a using the end plate 710. This will also be described in detail withreference to FIGS. 78 to 80(b).

Like the magnetic steel plates 701 a, the end plate 710 is, asillustrated in FIG. 79, of a hollow cylindrical shape around therotating shaft 11 and outer and inner diameters identical with those ofthe magnetic steel plates 701 a (i.e., the rotor core 701).

The end plate 710 is placed on one of axially opposed ends of the rotorcore 701. The end plates 710 may alternatively be disposed on both theaxially opposed ends of the rotor core 701. In the fifteenthmodification, the end plate 710 is mounted on the lower end of the stackof the magnetic steel plates 701 a which is located far away from theother end of the stack (i.e., the intermediate portion 45).

The magnetic steel plates 701 a and the end plate 710 have formedtherein the holes 707 extending through the stack of the magnetic steelplates 701 a and the end plate 710 in the axial direction. In otherwords, each of the magnetic steel plates 701 a and the end plate 710 hasthe holes 707 passing through a thickness thereof. The bar-shaped rivets708 serving as fasteners are disposed in the holes 707. The rivets 708also serve as stopper to hold the magnetic steel plates 701 a fromrotating or turning relative to each other.

The through-holes 707 are, as illustrated in FIGS. 77 and 79, locatedcloser to outer peripheral edges of the magnetic steel plates 701 a andthe end plate 710 than to the radial center thereof. Each of thethrough-holes 707 is, as can be seen in FIG. 77, located in the outerwall 704 of the magnetic steel plate 701 a in alignment with one of thedividing walls 706 in the radial direction of the magnetic steel plate701 a (i.e., the rotor core 701). In other words, each of thethrough-holes 707 is located to have the center thereof on the q-axis.

The number of the through-holes 707 is optional. For instance, thethrough-holes 707 are not necessarily arranged on all the q-axes, butmay be disposed on every other q-axis or every third q-axis.Alternatively, the through-holes 707 may be arranged at a given angularinterval of, for example, 90°, 45°, or 30° away from each other in thecircumferential direction of the rotor core 701.

Each of the rivets 708 has a length which extends in the axial directionand has a lower head (i.e., a lower end) protruding downward outside thelower end of the rotor core 701 (i.e., the end plate 710). The lowerhead (i.e., the lower end) of each of the rivets 708 has the flange 708a whose outer diameter is at least larger than the diameter of thethrough-hole 707 and which is engageable with the end plate 710.

The magnetic steel plates 701 a are tightly fastened or compressedthrough the end late 710 in the axial direction between the upper headsand the flanges 708 a of the rivets 708. In other words, the stack ofthe magnetic steel plates 701 a and the end plate 710 is firmly grippedin the axial direction by the rivets 708.

The end plate 710 has a wave shape in the axial direction in the shapeof a wave washer. FIG. 80(a) is a longitudinal sectional view whichdemonstrates the end plate 710 before being mounted on the magneticsteel plates 701 a. FIGS. 80(a) and 80(b) show the end plate 710developed in the circumferential direction and represent the wave of theend plate 710 on a scale increased for facilitating the ease ofvisibility of the shape of the wave.

The end plate 710 is, as illustrated in FIG. 80(a), waved in thecircumferential direction thereof. When the end plate 710 is, as can beseen in FIG. 80(a), placed on the end of the stack of the magnetic steelplates 701 a, it will make contacts and non-contacts between the endplate 710 and the stack of the magnetic steel plates 701 a.

The through-holes 707 formed in the end plate 710 are, as describedalready, arranged adjacent each other in the circumferential direction,so that they may be aligned with the dividing walls 706 of the magneticsteel plates 701 a in the radial direction. Locations of crests ortroughs of the wave shape of the end plate 710 are independent oflocations of the dividing walls 706. This will cause some of thethrough-holes 707 of the end plate 710 to be, as illustrated in FIG.80(a), located away from the lower end of the stack of the magneticsteel plates 701 a in the axial direction.

Accordingly, when the end plate 710 is fastened to the stack of themagnetic steel plates 701 a using the rivets 708, some of the flanges708 a, as illustrated in FIG. 80(b), press and elastically deform theend plate 710. It is preferable that the stack of the end plate 710 andthe magnetic steel plates 701 a is compressed by the rivets 708 to anextent that air gaps are still present the end plate 710 and the stackof the magnetic steel plates 701 a, in other words, the end plate 710still elastically works as a cushion.

Each of the rivets 708, as clearly illustrated in FIG. 79, has the upperhead which protrudes outside the intermediate portion 45 in the axialdirection and is staked or pressed using a nut on the surface of theintermediate portion 45. The locations of the upper head and the flange708 a of each of the rivets 708 may be reversed vertically. In otherwords, the lower end of each of the rivets 708 may be fastened to theend plate 710 using a nut serving as a flange.

The production method of the end plate 710 will be described below.

First, the plate strip 791 extending straight illustrated in FIG. 81 isprepared. The plate strip 791 is rolled or milled using a rollingmachine (also called a rolling mill) MA and then curved into a circularring shape having a given radius of curvature to complete the end plate710. More specifically, the rolling machine MA works to press or millonly one of outer side portions of a width of the plate strip 791 usinga roller to extend that side portion in a lengthwise direction of theplate strip 791, thereby curving the plate strip 791 into a circularshape with a given radius of curvature. The curving of the plate strip791 will create a wave having an amplitude in the axial direction. Afterproduced in the above way, the plate strip 791 is drilled to form thethrough-holes 707 in an outer circumferential portion of the plate strip791. The through-holes 707 are, as described above, arranged at a giveninterval away from each other in the circumferential direction of theplate strip 791.

Next, the production method of the rotor core 701 will be describedbelow.

First, the circular ring-shaped or annular magnetic steel plates 701 aare prepared and stacked to overlap each other in a thickness-wisedirection of the steel plates 701 a (i.e., the axial direction of therotor core 701) to form a first stack. The end plate 710 is placed on atleast one (i.e., a lower end in this embodiment) of opposed ends of alength of the first stack of the magnetic steel plates 701 a to form asecond stack with each of the through-holes 707 of the end plate 710aligned with a respective one of the through-holes 707 of the firststack of the magnetic steel plates 701 a. The rivets 708 are theninserted into the through-holes 707 of the second stack of the magneticsteel plates 701 a and the end plate 710. Finally, the rivets 708 arefixed. For example, the rivets 708 are tightened using nuts.Alternatively, the flanges 708 a of the rivets 708 are staked. Thispresses the end plate 710 in the lengthwise direction of the first stack(i.e. the thickness-wise direction of the end plate 710) to firmlycompress or grip the second stack of the end plate 710 and the magneticsteel plates 701 a in the axial direction (i.e., the lengthwisedirection of the second stack). A set of the rivets 708 and the secondstack is assembled with the magnet unit 700 to complete the rotor core701.

The above fifteenth modification offers the following beneficialadvantages.

The magnetic steel plates 701 a are gripped or fastened tightly in theaxial direction in the form of a stack using the end plate 710 and theflanges 708 a of the rivets 708. The use of the end plate 710 betweenthe flange 708 a of each of the rivets 708 and the stack (i.e., thefirst stack) of the magnetic steel plates 701 a distributes stressexerted by the flanges 708 a. The end plate 710 is shaped to have a wavewhich is elastically deformed in the axial direction thereof (i.e., thestack of the magnetic steel plates 701 a). This creates air gaps betweenthe end plate 710 and the end of the stack of the magnetic steel plates701 a and serve as cushions to absorb mechanical impact acting on thestack of the magnetic steel plates 701 a.

The end plate 710 is made of a sheet or plate whose only one of thesides is rolled. This facilitates formation of a wave shape of the endplate 710 undulating in the circumferential direction thereof. The endplate 710 is produced by machining the plate strip 791 into a circularring form, which achieves more effective production of the end plate 710than when a disc-shaped magnetic steel plate is stamped to form the endplate 710.

When the through-holes 707 are formed in the plate strip 791, afterwhich the plate strip 791 is machined into a circular ring shape, itwill cause the through-holes 707 to absorb distortion arising from themachining of the plate strip 791, thereby resulting in a decrease inamount by which the wave shape of the end plate 710 is elasticallydeformed. When the plate strip 791 is machined into the circular ringshape, it will usually result in a larger degree of elastic deformationof a radially inner side of the plate strip 791 than that of a radiallyouter side of the plate strip 791. For these reasons, the through-holes707 are formed in the radially outer side of the end plate 710 aftermachined into the circular ring shape, thereby achieving a desireddegree of elastic deformation of the wave of the end plate 710 to ensurea required ability of the wave shapes to function as cushions.

Each of the magnets 702 in the fifteenth modification is, like in theabove embodiments, designed to have easy axes of magnetization each ofwhich includes a first portion in a region close to the d-axis that isthe center of a magnetic pole and a second portion in a region close tothe q-axis that is a boundary between magnetic poles. The first portionis oriented to extend more parallel to the d-axis than the secondportion does. The easy axes of magnetization define magnet-producedmagnetic paths. More specifically, each of the magnets 702 has thearc-shaped easy axes of magnetization to define the arc-shaped magnetproduced magnetic paths, thereby minimizing a risk of leakage ofmagnetic flux from a portion of the magnet 702 far away from the stator50 (i.e., the armature) and enabling the outer wall 704 (i.e., the backyoke) to be thinned. Therefore, when the through-holes 707 are formed inthe outer wall 704 in alignment with the magnet chamber 703 in theradial direction, it results in a risk that portions of the outer wall704 in which the through-holes 707 are formed may be thinned and broken.

In order to alleviate the above problem, the outer wall 704 in thefifteenth modification is, as clearly illustrated in FIG. 77, designedto have the through-holes 707 each of which is aligned with one of thedividing walls 706 in the radial direction of the outer wall 704. Inother words, each of the through-holes 707 is located on the q-axis,thereby eliminating a risk that the dimension of the rotor core 701 inthe radial direction is locally decreased. Each of the through-holes 707is misaligned with a respective one of the magnet chambers 703 in theradial direction of the rotor core 701, thereby avoiding the localdecrease in thickness of the rotor core 701 (i.e., the magnetic steelplates 701 a), which eliminates a risk that the rotor core 701 is brokennear the through-holes 707.

The magnet-produced magnetic paths in each of the magnets 702 are of anarc-shape and extend near parallel to the circumference of the rotorcore 701 near the q-axis. The through-holes 707 are, therefore, locatedradially outside the magnets 702, i.e., the outer wall 704, withoutinterrupting the magnet-produced magnetic paths in the magnets 702. Thisminimizes a drop in output torque arising from the through-holes 707.

The rotor core 701, as described above, includes the outer wall 704, theinner wall 705, and the dividing walls 706 connecting the outer wall 704and the inner wall 705 together, thereby enhancing mechanical strengthof the rotor core 701 as compared with an SPM rotor core.

Variant of Fifteenth Modification

The fifteenth modification may be altered in the following way.

Each of the magnets 702, as illustrated in FIG. 82, has the far statorperipheral surface 702 which faces away from the stator 50. Each of themagnets 702 has the recess 730 formed in the far stator peripheralsurface 702. The recess 703 is located closer to the d-axis than to theq-axis. The recess 703 is hollowed inwardly in the radial directionalong the d-axis. The recess 703 extend in the axial direction.

The magnet-produced magnetic paths in each of the magnets 702 becomeshort in the region which is close to the d-axis and far away from thestator 50, so that it is demagnetized. The recess 703 located far awayfrom the stator 50 on the d-axis, therefore, hardly impinges on thedensity of magnetic flux, which enables the volume of the magnets 702 tobe reduced.

The outer wall 704 has formed on an inner periphery thereof theprotrusions 731 each of which engages one of the recesses 730. Theprotrusions 731 project from the outer wall 704 inward in the radialdirection of the outer wall 704 (i.e., toward the stator 50 or themagnets 702). The protrusions 731 lie on the d-axes, in other words,middles of the magnets 703 in the circumferential direction.

The protrusions 731 are fit in the recesses 730, thereby avoidingexertion of pressure by the magnets 702 only on the dividing walls 706in the circumferential direction. In other words, the dividing walls 706and the protrusions 731 serve to disperse the force produced by themagnets 702 in the circumferential direction, thereby eliminating a riskthat the force may concentrate on the through-holes 707 and the dividingwalls 706, so that the rotor core 701 is damaged or broken.

The dividing walls 706 in the fifteenth modification extend along theq-axes, but may alternatively be aligned with the d-axes. In this case,the magnets 702 are isolated from each other across the d-axes. Each ofthe through-holes 707 may be located to radially overlap one of thedividing walls 706 extending along the d-axes. In other words, thethrough-holes 707 may be disposed on the d-axes.

The end plate 710 in the fifteenth modification is made by milling theplate strip 791 using the rolling machine MA, but however, mayalternatively be produced in another way. For instance, the end plate710 may be made of a curled strip. Specifically, the end plate 710 maybe formed by bending or curling the plate strip 791 in thecircumferential direction.

The end plate 710 in the fifteenth modification may alternatively bedesigned to have the through-holes 707 located in places different fromthose described above. For instance, it is preferable that each of thethrough-holes 707 is formed in a portion of the end plate 710 which isfarthest away from the magnetic steel plates 701 a before the end plate710 is fastened to the magnetic steel plates 701 a using the rivets 708,in other words, where an amount by which the end plate 710 iselastically deformable is maximum. In the example in FIG. 80, thethrough-holes 707 are preferably formed in portions of the end plate 710which are located farthest away from the magnetic steel plates 701 a.

The rotor 40 in the fifteenth modification is of an IPM type, buthowever, may alternatively be designed as an SPM type of rotor 40, asalready described in the above embodiments or modifications.

While the present invention has been disclosed in terms of the preferredembodiments in order to facilitate better understanding thereof, itshould be appreciated that the invention can be embodied in various wayswithout departing from the principle of the invention. Therefore, theinvention should be understood to include all possible embodiments andmodifications to the shown embodiments which can be embodied withoutdeparting from the principle of the invention as set forth in theappended claims.

What is claimed is:
 1. A rotating electrical machine comprising: amagnetic field-producing unit which includes a magnet unit and amagnetic core, the magnet unit being equipped with a plurality ofmagnetic poles arranged to have magnetic polarities located alternatelyin a circumferential direction of the magnetic field-producing unit; anarmature which is equipped with a multi-phase winding; and a rotor whichis implemented by one of the magnetic field-producing unit and thearmature, wherein the magnetic core is made of a stack of a plurality ofannular core plates and an annular end plate, the annular core platesbeing disposed on each other in a form of a stack with axially opposedends, the annular end plate being mounted on at least one of the axiallyopposed ends of the stack of the annular core plates, wherein the coreplates and the end plate have formed therein through-holes which extendthrough the stack of the core plates and the end plate in an axialdirection thereof, wherein fastening members which are of a bar shapeare disposed in the through-holes, wherein each of the fastening membershas a flange on an end of a length thereof, the flanges of the fasteningmembers engaging the end plate to tighten the core plates in the axialdirection, and wherein the end plate has a wave shape which isdeformable in the axial direction.
 2. The rotating electrical machine asset forth in claim 1, wherein the end plate is made of a rolled stripwhose outer side portion is milled or a curled strip formed by bending astrip in a circumferential direction of the end plate.
 3. The rotatingelectrical machine as set forth in claim 2, wherein the through-holesare located closer to an outer peripheral edge of the end plate than toa radial center thereof.
 4. A production method for producing a rotatingelectrical machine which includes: (a) a magnetic field-producing unitwhich includes a magnet unit equipped with a plurality of magnetic polesarranged to have magnetic polarities located alternately in acircumferential direction of the magnetic field-producing unit; (b) anarmature which is equipped with a multi-phase winding; and (c) a rotorwhich is implemented by one of the magnetic field-producing unit and thearmature, the method comprising: preparing a first stack of a pluralityof annular core plates; mounting an annular end plate on at least one ofopposed ends of a length of the first stack of the annular core platesto form a second stack; inserting bar-shaped fastening members intothrough-holes extending through the second stack in a lengthwisedirection thereof, each of the bar-shaped fastening members having aflange on an end thereof; and tightening the fastening members to havethe flanges pressing the end plate to grip the second stack of the coreplates and the end plate to complete a magnetic core assembled with themagnetic unit of the magnetic field-producing unit, wherein the endplate has a wave shape deformable in a lengthwise direction of thesecond stack.
 5. The production method as set forth in claim 4, whereinthe end plate is made by milling one of outer side portions of a widthof a strip or by bending a strip in a circumferential direction of theend plate.
 6. The production method as set forth in claim 5, wherein thethrough-holes are formed in the one of the outer side portions of thestrip, after which the strip is machined to complete the end plate.